I don't agree. Well, I think there was a change of spirit, but it's not a darker spirit that irks me, it's the more... "epic action-packed" movie one, ME1 had a much, much more old school sci-fi feel and music than ME2 which I loved its dark feel. Plus, while I preferred the shooting mechanics in ME2, the missions and overall level design is a huge step down, the game feels more like an actual third person shooter than a rpg/shooter hybrid. If you compare ME1's and ME2's missions, you notice how everything is streamlined, lacks interaction and mini-quests, and is just corridors after corridors compared to ME1.
Plus, you can be right with good characterization, except for Shepard, he's even worse than in ME1. He has no depth at all, there's no grey road, you either are st. Peter saving the galaxy from the all consuming evil, or the worst jerk in the galaxy, where's all the choices and characterization of KOTOR? At least choices meant SOMETHING, there were consequences, now since gamers have to have everything, you give the same possibilities (and same everything) to paragon and renegade players, which is pretty much all you can be, you don't feel like making choices in conversations at all, go play KOTOR, you'll know what I mean.