Cataclysm has given WoW the tune up its needed. You even get to use your brain again. No more mindless AoE in Heroics.
Graphics: Still pretty outdated but not that bad.
Sound:Really good. The new musical score sounds very epic compared to Vanilla WoW, BC, and Wotlk. There is even remixes of the old Vanilla music. The sound quality is very good too.
Story: As you probably already know, Deathwing has reemerged from deepholm and literally raped Kalimdor and the Eastern Kingdoms. What you might not know is that Ragnaros is back and his buddies Al'akir and Neptulon are with him. Iso'rath, one of the servants of the Old Gods has appeared in the Twilight Highlands. Cho'gall and his Twilight's Hammer clan are on the move. To make matters worse, now that Garrosh is warchief the War between the Horde and the Alliance has gotten more intense.
Gameplay: The mechanics are mostly the same as before, but the game is a lot more fun. Blizzard has made lots of creative quest and much more challenging dugeons. There are five new leveling zones for high level characters. There is also a sixth pvp zone known Tol Barad. Tol Barad is pretty unbalanced and needs some changes though. Its practically impossible for players who are trying to attack and secure it to actually win. The first faction to own it tends to own it 95% of the time. There are seven new dungeons and 3 new raids. There are also two new bgs.
Conclusion: any WoW player should get Cataclysm. It's and awesome expansion that has redeemed WoW.