In November of 2004 Blizzard Entertainment released "World of Warcraft" to record sales. As time went on they've continued to add to it via content patches, including adding Battlegrounds in patch 1.5 on June 7th, 2005, and the latest content patch (1.6) which arrived on July 12th, 2005.
But before we go there, let's go over the basics.
World of Warcraft (or WoW for short) is a Massively Multiplayer Online RolePlaying Game or MMORPG. This means that you play on one (at a time, at least) of a number of servers with thousands of people on at the same time. That's the first choice you have in WoW: what type of server you want to play on.
PvE servers are "Player versus Enemy" servers. This means any PvP (or Player versus Player) combat is completely consensual, either by flagging yourself using the /pvp command, attacking a PvP-enabled enemy (indicated when you target them, and tend to be enemies such as city guards), by buffing (casting beneficial spells) or healing a friendly player who is PvP-flagged, or entering a Battleground or other PvP enabled area. These are the "standard" servers.
RP servers are PvE servers that have an additional "Role Play" rule set. These servers encourage people to use background lore appropriate names, talk in character (note: this does NOT mean speaking in Olde English), and to make the game more immersive.
There's an upcoming server set coming out that will be "RP PvP", a choice that has been much-requested. It'll be interesting to see what the populations look like on them.
After choosing your server, you select which side you want to play. In the WoW universe, there are two basic sides: Alliance and Horde.
The Alliance is made up of humans, gnomes, dwarves, and night elves. They've traditionally fought against the orcs and their allies, and in the last Warcraft RTS (real time strategy) game Warcraft III, they fought against the undead Scourge as well.
The Horde is made up of orcs, trolls, taurens (large cow-like creatures) and undead. The undead aren't the Scourge from Warcraft III but rather the Forsaken, a branch of the Scourge that have rebelled. The orcs have recently thrown off their racial curses and attempted to form a new society.
There are other factions you'll run into in the game as well - groups such as the Argent Dawn and the Venture Company, with various races, the goblin cartels, etc. - but right now you cannot play them. However, as you help or hinder them, your reputation with them will change, thus making goods cheaper or causing them to attack you on sight.
After you select side and race you pick a class that you wish to play. There are a number of classes, most of which can be played by both sides - though each side has one "special" class. These classes are rogue, priest, mage, warlock, hunter, warrior, druid, and the special class - paladins for the Alliance, and shamans for the Horde.
Each class has their own set of abilities and skills. You start off with just a very basic couple of abilities. As you do quests and kill monsters, you gain experience points, which will cause you to level up. As you level up to a maximum of 60, you get the chance to buy skill upgrades from your trainers, learn new abilities, and starting at level 10, get points in "Talents" which further customize your character. Also, as you level up, you can get better equipment, making you more powerful.
You can also do various "crafts". There are three secondary crafts, which anyone can do. These are First Aid (which gives the ability to make bandages and anti-venom), Cooking (which allows you to make food to regenerate your health and give some minor buffs), and Fishing (which catches fish, some of which are good for alchemy, as well as potentially get other items).
You can have up to two "primary" professions. These are taken from a somewhat longer list such as herbalism, alchemy, leatherworking, skinning, blacksmithing, mining, engineering, tailoring, and enchanting. These can allow you to collect resources (mining, herbalism, skinning) or make items. Some are better combinations than others. For example, hunters often take mining and engineering in order to make their own bullets, while herbalism and alchemy is also a popular combination to make your own potions.
So what do you during the game?
Well, before you hit level 60, you will primarily be doing quests. As you venture through Azeroth's two continents (Kalimdor and the Eastern Kingdoms) you'll find a variety of NPCs (non-player characters) who will have quests for you. You'll know that by the fact that they have a golden "!" over their head (or a silver "!" if they have one in the next couple of levels for you). You can take up to 20 quests at a time, and you can know your status with any NPC by seeing if they have a silver "?" over their head (indicating you haven't finished your quest yet) or a golden "?" (which means you're done). Quests will typically give you both experience points and items or gold.
Quests take many forms. Many of them are simply "delivery" quests - take this item from one person to another. Some involve making items. Others might have you gather items. Sometimes you have to interact with NPCs and talk to them. Most involve killing one or more bad guys, and as you go up in level, more and more will involve going into various dungeons.
You also get XP (experience points) from killing mobs or creeps - i.e., computer controlled enemies. WoW includes a "rest" mechanic, so if you only play irregularly, or camp regularly in a town inn or a capital city, you will get twice as much experience from each enemy you kill for a set amount of time.
Mobs also drop items and coins, and some beasts, when dead, can be skinned by people with the skinning profession.
Dungeons in WoW are often instanced. When you enter them, only you (and the people in your group or raid (a group of groups)) will be in there, so there's no competition. In instances most of the enemies will usually be called "elites". These are tougher than an equivalent level enemy, thanks to additional abilities and hits.
If you don't get the items you need for your character from quests or drops, you can get them from other characters. You can talk with them to find out about trading, for example, giving gold and items to a blacksmith for him to make you a new weapon or piece of armor. More often though people go to the Auction House, of which there is one for each side, and one that sells to both sides. There, people can put an item up for auction, and it helps facilitate the economy of the server.
Good usage of the auction house can make your character a lot of money - though overusing it can also cause to go broke. You want to save your money as you hit level 40, since at that level you can get a "mount", a horse/ram/cat/etc. that helps you travel faster. For most characters, this costs 90-100 gold - however, paladins and warlocks have quests to get "free" ones. At level 60, you can get an even faster mount that goes for closer to 1000 gold (usually 900 after reputation discounts).
So what do you do at 60?
Some people continue to quest, kill mobs, work on their professions, etc. Others continue to look for new places to explore. Along with that, most people do one of two things: raid and PvP.
Raiding means getting a group of groups together - anywhere from 2 groups of five (the biggest allowed group size in WoW is 5 people) to 8 groups. They then go to an instance and attempt to work their way through, confronting various traps, puzzles, and very very powerful mobs in order to get very good loot. There are also a couple of outdoor, non-instanced "boss mobs" that serve the same purpose.
With the addition of the June 7th 1.5 patch, PvP became a much more popular choice because it introduced the Battlegrounds. Don't get me wrong - you don't have to be 60 to do the two different Battlegrounds (Alterac Valley and Warsong Gulch). However, it seems that most people wait until then.
Warsong Gulch tends to run the most, thanks to the smaller requirement of people. (The Horde is outnumbered on many servers, meaning that the queues for Alliance people into the BGs can be quite long.) It's a basic "capture the flag" type of mechanic.
Alterac Valley is a more protracted battle, featuring strong points, grave yards, and towers that can all be captured. In AV, you can even at some points call in air strikes, cavalry raids, and large elementals.
In both, them you build up faction with your side by doing quests and looting enemy dead. The looting mechanic is a bit disadvantageous for ranged damage dealers such as mages and hunters, since they have to run to pick up the loot and it's "free for all" as to who gets it. (Against traditional computer opponents, only the person who damaged the mob first, or tagged it, gets the loot.)
The quests can give out some powerful items. In addition, you get honor points by getting kills, capturing flags, etc. These raise your rank in proportion to the rest of the server. Therefore, if you gain 1000 in one week, you'll go up in rank faster on a server where the average character only gained 100 versus a server where the average character gained 1000. As you go up you can buy new, more powerful armors and weapons.
To get into the BGs, you have to enter a queue. The game won't start until the sides are (vaguely) even and will end early if too many drop on one side. These queues, particularly for AV, and on the Alliance side, can last for many hours.
In addition, some gamers prefer to be anti-social in the BGs and only play for their own betterment instead of for the team. Thus, so far, the BGs have been a very mixed bag for most players. One addition that will probably help them in the new patch (July 12th) is that you can enter the queue from a major city, so you don't have to travel far to get into the BGs. And while in the queue, you can continue doing whatever else you were doing, and when it's your turn, you'll get an opportunity to be teleported to the instance.
So that's the game. Let's look at some of the more specific parts of it.
GRAPHICS: Blizzard went with a "cartooney" type of graphics for the game. This actually works out very well with the storyline and style of the game. Some people, looking for ultra-realistic graphics, might be disappointed, but soon you'll find that it just works.
SOUND: The sound isn't overdone. In most zones you get a short bit of sound and then only some snippets here and there, plus the ambient sounds of the areas. It's very important to have good stereo sound - it'll help you find enemies, detect traps, etc. It's just well done.
USER INTERFACE: It's very easy to modify the interface if you know how, and so there are a large number of "mods" you can download to help your game. For example, some will help you control your pet (if you're a hunter or warlock), give you more hotbars for skills, or keep track of which mining nodes you've found.
STABILITY: Unfortunately, Blizzard has had some well-known problems with stability. The game is much better now than it was just after launch, but some areas - such as Ironforge, near its Auction House - have very bad lag, and there are still issues with things such as the boats between continents dropping people into the ocean.
BUGS: There are also still a number of bugs, and while each patch fixes a number of them, more are introduced. These can be anything from mining nodes appearing in mid-air, to the master looter system (for determining who in a group or raid gets loot) bugging and allowing someone to steal the loot, to enemies attacking through walls. The game is huge, so there are lots of places where these can show up, but Blizzard does work on them.
EXPANDED CONTENT: Every month or so Blizzard will put out a new patch with more content. They've added new recipes for professions, new enemies, new graphics, new dungeons, and more. For holidays they'll often have special things show up, such as snowball fights near Christmas and easter eggs at Easter.
So what of the game?
Well, like all games, it has a learning curve. However, to me, WoW has felt like a much more beginner and casual gamer friendly game than others. And while it does have its share of blood and even occasional bawdy jokes (check out the /flirt and /silly emotes for the characters) a lot of parents consider it kid-friendly, too. (Though keep in mind that other players might be bad people.)
In short, if you're looking for an MMORPG-style game, and are willing to pay the monthly fee, you should definitely give WoW a shot. If you played before, maxed out your level, and got bored, the Battlegrounds and new dungeons will give incentive to come back, but keep in mind that thanks to queues and the such that right now they're not necessarily the best incentive to come back.