I enjoyed the first game immensely when I first played it: The atmosphere and story were great, but often found the combat/dungeons/and character progression to be pretty dull and tedious. It's funny, because I didn't really realize that until I played the second game, which (as was pointed out), was a lot weaker, story wise, but seemed to be improve on pretty much everything else from my perspective.
Sure, it was a lot more "linear" in appearance, but the first game just kind of gave you the illusion of making your own path. And the rover missions? Cool for about the first three, and then very, very tedious.
I can see where you're coming from, but I certainly found the second (and now the third) more engrossing. To each their own, I guess.
Also, addicted to the MP in the third. Oh, and Vanguard kicks ass in single player now. Carry a light load and spec for quick power recharge: blast in, fire ammo shotgun, fire ammo shotgun, weird biotic ground pound, and then heavy melee anything left standing with a fist of dark energy to the face. aaaaaaand blast out right away if you need to. So satisfying.
I've literally cleared rooms by blasting from mofo to mofo.