Best MMORPG ever.. just ask the 8 mill that play it. It offers great gameplay, combat, competition, and is in one fluid world. Its addicting as **** and is great fun. You wont be able to stop playing it... except maybe to play css

The pvp is extremely advanced with many styles including world pvp (ganking noobs) and battle grounds (10v10, 20v20, and 40v40 and in the xpack 1v1,2v2,5v5 and 60v60???? not sure about 60v60 but lets hope!)
The pve in wow is also fun with long raids which require skilled noobs and Night Elves (lol j/k) to do. But ya they are fun, challenging, and you get 1337 gear from it and popularity if you are the first one to complete the raid.
Other good things include: OK graphics, minimal lag, and LOTS of patches and bug fixes. Blizzard definetly spends time and pays attention to keeping this game awsome.
You also get alot of freedom in the game. You can be on either 2 sides: horde or alliance (which fight each other) and choose from 8 classes: Mage, Warrior, Rogue, Hunter, Warlock, Priest, Shaman, and Paladin. There are also four races for each faction: Alliance- human, gnome, Night elf, and dwarf Horde- Troll, Tauren, Orc, and undead. Also within each class you can completely customize your style of play using 3 unique talent trees to make your character fit your strategies. ie: hunters can spec themselves to be good marksmen... or they can improve their beastly companion to do loads of ownage. Its up to you!
Drawbacks: leveling can be slow if you are casual, also the game seems to rely on balance of time played 70% and skill 30% although this will change in the xpack to about 50-50 aperantly. The biggest drawback of all however is probably the $12 a month... but IMO its worth it. Instead of buying $50 xpacks for other games every 4 months you get awsome service, gameplay and good fun.
Common comparisons: Guild wars, runescape, everquest. IMO none of these compare to WoW. Having played GW and RS (sadly) they got boring within days and you didnt have as much choice. WoW greatly owns GW and RS in PvE and PvP. I cannot say about Everquest only having played the demo but im sure WoW would be better

Anyone looking to join me and the others that have it go to:
Us server: Altar of Storms
Faction: alliance
Guild: Gnomes in a Toaster (soon to be changed)
and get to 60 be4 X-Pack!
For more info on teh leetest RPG around go to www.worldofwarcraft.com