If you want some real "Role Playing" in your games, then I cant recomend
Planescape Torment enough, it is IMO the best RPG ever and the best written game of any kind. The role-playing, chacters, dialog, setting, and plot are exeptional. Theres a lot of reading involved so if your a hack-n-slash person this wont be your cup of tea. Good luck finding it though, it recently officaly went "out of print"

for some mad reason as it's only 3 years old (my guess is some licencing issue, also although criticaly acclaimed it sold criminaly poorly) but some shops may still have it, or you could probably find it second hand.
Other classic Interplay RPGs include
Fallout 1 & 2 they are post-apocalyptic RPGs with exelent character creation/ development loads of side quests, and the freedom to be good guy or be a real basted, a reputaion and karma sustem ensured the choices you make do have consequences. The second one especialy is massive. The combat is very refeshing if you tired of swords and magic, now you can have some real hardware: rocket-lauchers, machine guns, automatic-shotguns, assult-rifes, plasma weapons, you name it.
BTW they are both quite dark and moody (athough not without humour), but then again I like dark and moody games
here are some-links:
Interplay website
Torment review
Fallout 2 review