Well, it was here on Tuesday in the early AM, and it certainly has taken over the lives of many around it already, I'm sure. I myself picked it up and have been playing it like crazy ever since. I'm of course talking about Cataclysm.
I thought I'd offer a brief review and summary of my feelings about the game. Let me say this... if you previously played WoW (Vainalla or BC or even Wrath) you will certainly be aware of how the things that made WoW a really fun game have been slowly slipping away. This was most true in Wrath, as the game became very easy in a lot of ways, grind heavy, and just plain boring. Well, let me say this. Blizzard clearly must have got this... because Cataclysm has made WoW into a new fresh game again... full of fun, challenge and the wonder that the original held.
You can really tell that a huge amount of work was invested... clearly more work than previous expansions. Questing for one is actually fun and interesting, and the lore elements are awesome. There is usually a 'massive event' at the end of each of the new zones once you complete the quests, culminating the progress you have made. It's really cool to watch the events unfold and see the fruits of your labor (or the smoke from your destruction).
Dungeons are challenging... and news flash - CC IS BACK! Love it. Then you hit 85, step in your first heroic, and prepare to face your greatest challenge since well... as long as you can remember. Even with an all-guild group, with coordination and teamwork, not standing in the fire and all that jazz, you will still get pooped on. A lot. A lot a lot. These are harder than Burning Crusade heroics. By a long shot. There's no way the average "scrub" will ever complete this in their current implementation.
The whole atmosphere has shifted, and the game just has a different feeling now. Guild achievements, leveling, and perks are awesome. The perk you unlock at guild level 2 is 'Fast Track' which gives everyone in your guild 5% more xp from quests/kills. This helps a lot for your slower levelers and helps everyone, even lower level alts. Guild reputation is a mechanic put in place to help guild loyalty. There are rewards you have access to based on your reputation with the guild, which takes a long time to increase and everyone starts at neutral. So if players guild hop they'll never unlock the cool stuff.
Anyways, I could go on forever talking about this game... but I don't need to. It's just simply amazing. If you were considering, or debating at all... stop. Just go out and get it. You won't regret it.