When Bal started talking about how Cataclysm would see cool things happen for Shamans because it was about elementals and shit, I thought he was wrong because 1) lorefag and 2) Shamans haven't improved since they lost Spirit of Wolf back in Warcraft Adventures. But it turns out they get the best new spells overall, the single best spell in Spiritwalker's Grace, the best potential spells in Earthquake and Spirit Link, and the best Mastery bonus in Elemental Overload. And if history is any indication, they'll keep their distinction of Overall Best Tier Sets.
Second place is a tie between Warlocks and Hunters. The death of shitty, old mechanics is the most exciting thing about Cataclysm, and 'soul shards', 'ammunition', and 'Hunter mana' were all in the top 5; exact placement varies per person. (the other 2 were 'weapon skill' and 'combo points not carrying to other targets'. 4.5 out of 5 ain't bad.)
Druids probably get the next nod, with a long-overdue interrupt for Ferals, ToL becoming a cooldown so we can actually see Druid gear outside of Dalaran Orgrimmar, being the only class to gain a dispel category without losing anything, arguably the largest benefit from haste of any healer, and the baking-in of Eclipse. Oh yeah, and their AoE spell is a mushroom. Should make old content Freya kills enjoyable at 85...
Death Knights come next, or so I have been led to believe: refining of rune mechanics and consolidation of talent tree roles, a convenient method of getting diseases up, Anti-PW:S Strike, and a spell reflect equivalent. Hey, Warriors use spell reflect a lot, right?
After that it's a bit hazy. Priests get Life Grip and Power Word: This Sure Would Have Been Nice For The Lich King, but boring Mastery bonuses. Having said that, there is a lot of potential in things like Holy spec 'empowered state' healing and something regarding Shadow Orb consumption. Time will tell.
Rogues get a half-measure that deals with combo points, which is better than what they've had for the last five years, and then.. some defensive cooldowns and a self-heal. I think Rogues may benefit more from the actual talent tree revamps themselves. This is probably true of every class, to be fair.
I won't touch on Warriors because Hraedon loaned me some Primordial Saronite recently and I think I owe it to him to not reopen old wounds.
Lastly, Mages. The most boring class gets the most boring preview. If Bloodlust + Drums of Speed are the most interesting thing you get—and in this case they are—you have problems as well as my condolences. But like I said on my guild forums, if you are playing a Mage, you are already well-accustomed to boredom. I wonder if new Ragnaros will be fire-immune!