Pre-Cataclysm, I was leveling via retribution (2h). I had a good rotation down, it worked quite well.
At some point, consecration started costing ~50% of your base mana? Ugh. And it seemed to take more mana and time to kill a single mob.
Before reaching 80 I switched to protection (shield/1h) and finished my last level before attempting the new areas. Even before reaching Cataclysm content, protection feels like retribution did, after a mob is dead -- full mana and maybe a little reduction of hp.
Cataclysm mobs are pretty tough, one on one - no problem, more than one... some healing is necessary, maybe a bubble once in a while. Generally -- not having too much trouble. Still ending up full of mana when the mob is dead.
One frustrating aspect is that so many of the protection spells are AOE and Cataclysm seems to have those non-aggro mobs around the aggro mobs and even though I am only attacking one, I end up fighting 2 or 3 (when you're in water, the spells end up pulling something over your head as well).
I have several characters and from playing one of them at the launch of the expansion, I think Blizzard has tuned the mobs back a bit so I'm not sure I can accurately portray how well I'm doing as a protection paladin.
After getting a few upgrades in the initial Cataclysm areas, each toon generally levels out and can handle the mobs much better (example: level ~174 to ~224 armor is a huge jump in stats, especially in the stamina department). I point out stats because starting out in Cataclysm, I was only at 14k hp and about 5k mana.
The first toon I played on launch (that was 80 of course) was a shaman. I simply tore through the content (Vashj'ir). It was a shock at first how hard they were hitting but the spell procs that kept going off giving me free heals reduced the sting quite a bit.
The second toon I tried in Vashj'ir -- the deathknight. I suppose this is where I really noob it up. I didn't think I would have trouble with the deathknight. Ouch. For some reason I cannot get the hang of it, a single mob is beating the absolute crap out of me and I have far more armor than any of the other toons. More than one mob? Probably dead. I know Blizzard has made some changes to the deathknight that people aren't happy with so I'm not sure what to do. I was using frost specialization but it doesn't seem to be what it was.
The third toon for Vashj'ir -- the paladin. As I stated previously, not too much trouble.
Cataclysm is very entertaining. Blizzard has really got the compartmentalizing thing down (taking you into your own instance for quests, focusing on you) and it really brings the story out and it sticks with you. Much like starting a deathknight, starting a Worgen is quite entertaining.