OP asked for good depth of story and character development, neither of which TOEE or TQ have. I'm not saying everything sucks other than BG2, but IMHO BG2 is miles better than either of these two games, different genre or not.
TOEE has a very similar playstyle to BG2, true (they are both AD&D games), but thats about the only thing they have in common. IMHO TOEE has a very cliched and simplistic linear storyline, pretty much the standard RPG fantasy fare. Character development was nonexistant - you could recruit party members, but they are pre-created and didnt have any relevance to the plot or any backstory, they were just there to effectively help you kill things better. Plus the game was annoyingly, game-breakingly buggy.
TQ is ok if you like action rpgs (although I think Diablo 2 and Dungeon Siege 2 are a lot better), not much to it other than hacking down thousands of creatures and collecting huge amounts of loot, which can be fun.
BG2 is a thing of beauty - it has a long, interesting and twisty storyline, great characters, locations and monsters, and a brilliant cast of NPCs. Players in your party can be interacted with, you can talk to them and your relationship with them develops according to what you say and do (you can even have a gay relationship with one of your party!), there are loads of varied and interesting quests (that dont always involve killing things, like a lot of RPG quests tend to do) - you develop a real emotional attachment to them, its the only game I've played where I've experienced this (apart from maybe the KOTOR games). It's epic, immersive, enthralling and addictive - to me BG2 is the benchmark for all RPGs. (I haven't played Planescape Torment but I hear it is also good in this sense.)
Enough drooling from me