ME2 suffers so much from only existing because they said it would be a trilogy though, you know what I mean? Like nothing really happens with the core story that was set up in ME1. We just kill time with some collectors and cerberus while waiting for the reapers to get closer. ME2 does a lot right with gameplay and characters, but man the overall main story of that game bums me out too much, I think I actually prefered 1 in the end.
Honestly it's ME3 that suffers from being a trilogy right at the outset more than ME2, because neither of the two previous games did enough set-up for the Reaper's return or the mechanism for their defeat. ME2 is just kind of its own thing, and succeeds or fails on its own merits. If they hadn't promised a trilogy, this would have been fine, but they did and as a result ME3 had to tie up every single loose end, solve the Reaper plot and give closure to the series and characters. If ME3 was just another entry in the series, but not the
final one, it wouldn't have had so much weight to bear, and could have focussed on setting up the finale and closing some, but not all of the unresolved plot threads. Solving the Genophage and Quarian/Geth scenarios were the high point of ME3 in terms of writing quality, yet both felt like they were forced into an implausible scenario. The galaxy is under attack, time to get petty, dig our heels in and do stupid shit or demand concessions.