Well, most of us HAVE been playing the jesus out of this game, it's only natural that we'd get tired of it.
Talking about ME1 however, I disagree. Combat in ME1 was stale, and slow paced, and not intuitive, animations were, for the most part, klunky. As for replaying ME1 to get varying storylines, those are MUCH more limited in variation than what we've got in ME2.
Taking Archangel to go recruit Mordin nets you a lot of different dialog than taking Jacob, persay, just as much as taking Zaeed and Grunt to go recruit Archangel nets you interesting conversations, that would NOT be there with any other character.
And then there's the combat in ME2, with playing with different evolutions of powers, playing battles with different heavy weapons, and such, then of course, with the suicide mission, and different people to bring, and of course with the greater variation in ME2's plot.
It sounds like you're just upset at losing upgrades with NG+, which well, so am I.