What an amazing game. I want to say I haven't thoroughly enjoyed a game like ME2 in 5 years, but I had the same to say about Dragon Age so I'm afraid it's only been a few months.
I loved the removal of the inventory system but since there are only like 10 guns in the game and each is a straight upgrade, the whole idea of a weapons locker seems kind of pointless. If there were more sidegrade weapons, having a locker would be useful but there is no real reason to have one besides choosing your favorite heavy weapon.
Loved the removal of the Mako, didn't like the planet scan system too much.
Loved the removal of elevators, didn't like how there was so much less ambient/random/smalltalk conversations and just... general interaction with your team. The quality of conversations and voice acting is way up there, but it feels like there is so much less to talk about with your teammates as compared to DA:O. The characters are well done almost entirely across the board. They have motives and personality and depth and there's just so little I can do with them.
Taking Legion aboard the Migrant Fleet, for example, felt kind of underwhelming to me. There were what, three modified lines as a result of bringing this huge affront onto their mothership? Other than my gripe of quantity, the quality of dialogue and acting was pretty spectacular:
It was completely spontaneous and so unexpected that I completely lost it. There are some fantastic lines out there but you really have to dig to find them (talk to C-Sec customs about geth infiltration with legion in the squad for example).
Love the new combat system but hate the broken game balance at the higher difficulty levels. My biggest complaint with ME1 was that combat felt completely unfulfilling. My biggest complaint with ME2 combat is now that Adepts and biotic-focused characters are virtually useless at higher difficulties because everything has multiple health bars that make biotics useless until you remove them.
You need to use warp over and over to remove barriers then overload over and over to remove shields then warp over and over to remove armor and then you can finally start damaging health on one tough enemy... or you could just grab a sniper rifle and spam headshots, killing everything with monumentally less effort. Combine with adrenaline rush for example and you have a recipe for a much easier time.
Loved the ending and the control I had over who lived and who died. I finished my first playthrough at like 6 in the morning and just wanted to finish the last battle so I didn't put much thought into who I assigned to what task. I came back the next day and Nobody got Left Behind.
Loved the way side missions didn't suck, but hated the way the entire game basically felt like side missions and then abruptly swapped to the final battle and then the game was over.
I'd type more but I could be playing instead. Game is excellent.