A recap of some random thoughts:
ME1 Soldier: Bog-Standard
ME2 Soldier: Also Bog-Standard but AR is Cool
ME1 Adept: Face-Rape
ME2 Adept: Still Face-Rape Except on Higher Difficulties
ME1 Sentinel: Friggin Useless
ME2 Sentinel: Friggin OP
ME1 Infiltrator: Frustrating
ME2 Infiltrator: Slightly OP with Fun Additional Variant (CQC)
ME1 Engineer: Boring
ME2 Engineer: Limited but Sometimes Entertaining
ME1 Vanguard: Hilariously OP
ME2 Vanguard: Hilarious
It bugs me that loads of annoying people in the BW forums complain about how biotics got "nerfed" in ME2 and how they're "practically useless". According to these idiots, biotic classes are only good for Warp spamming because that's what kills protection layers, since most other biotic powers are only usable when an enemy is down to just health. If you're playing on Hardcore and Insanity - and there's no reason you shouldn't, you lazy bum - biotics seem like they aren't as good for widespread use anymore.
Except...biotics were memorably ridiculous in ME1, and are still pretty friggin ridiculous in ME2 on lower difficulties. Most missions are trivial as a biotic class, especially the Suicide Mission, which goes from being the defining moment of gameplay to a Throw fest where you can just knock Collectors off platforms willy-nilly. Even on higher difficulties, complaints that biotics are useless until enemies get down to health are outrageous. For one thing, health is the biggest bar that an enemy has. Not graphically, but in terms of actual points. For another thing, no weapons have special modifiers against health, unlike armor, barriers, and shields. Complaining that biotics are "only" useful against health is missing the point.
Besides, anybody who complains about useless biotics needs to play as a Sentinel and ride through Insanity on a goddamn palanquin with zero trouble at all.