Um outside of Omega, Illim and the Citideal are pretty weak. The citadel is is basically a strip mall with a transport system and Illim is a crappy maze of crap that likes to tease you with some awesome city background but you don't actually get to visit that city now do you.
Omega gets a pass because the sheer amount of time put into its development is awesome. It feels like an actual backwater space hub. I dear say the game should have just had Omega and scrap the two other boring towns/areas. Omega itself would have been better bigger. Theres obviously more to it then some club. Illium and The Citadel are just weak and boring.
People complain how liner FFXIII is, but I bet its story is better paced then ME. And ME isn't some big open world game, OMG you have some choice in the order of missions! Sure you can do some side missions but outside of the loyalty missions(which really are basically main missions) most of them are boring. Sure the one where you decide the where missile is is actually interesting but most are just go here and shot and stuff. Yeah I don't find fighting robots before they destroy some crates to be really interesting.
Also ME's story is far from great. Its pretty weak with a pretty dumb payoff and how the payoff gets there is the dumbest thing I have ever seen. The characters and their story is far better. I'm sure FFXIII will also have a good cast of characters that will actually tie into the plot, something ME 1 and 2 did not have. The the thing is FFXIII's characters will actually look decent.
I doubt FFXIII will not have atmospheric areas also.
Omega is interesting, but its just a club and some dealers. Its just really atmospheric. The game should have just had Omega, only bigger with more to do in it. The Krogan world is just brown and rubble. Not interesting at all,but its just a level and not a town. There are far better levels in the game. Such as the Migrant Fleet, levels on Lilium. and Omega itself. The Citadel is really boring. It is just a strip mall with 3 levels.