At the risk of getting off topic, I don't understand all the backlash against the original ending. I guess there were two main issues- one people wanted shepard to survive (apparently he can if you unlock a particular ending). Which I don't really get. Having shepard sacrifice himself and become a legend in the universe I thought was an appropriate way to tie things up. I mean there isn't a 4 coming. The trilogy is done, did people want shepard to retire and have kids or something? Doesn't make sense to me.
The other issue was people felt like there was no synopsis for the other characters. This I understand more because you've develop relationships with your crew, you are genuinely interested in their fates. But again I'm not too torn up about not knowing what happens to them because it's the end and the main story was about shepard and the reapers.
If you want to talk about potential I'm not sure what exactly you're getting at. The combat was improved, the powers and talent points were improved. I was a little disappointed they didn't develop the conversations and relationships more, it was basically the same options as 2.
Shep can survive if you gather more than X war assets; originally it was promised that you could acquire enough points for it via single player only if you did everything. This turned out to be false; it was originally impossible to obtain enough points without playing some degree of multiplayer (Extended Cut lowered the requirement to a level where you could get it, and the DLCs have made it much easier to get to that point).
But that's secondary. The whole backstory to the Reapers was frankly stupid, and you didn't even learn that much about them, so their origins were still pretty heavily shrouded in mystery. The only real thing you learned was why they were created, and that is a terrible, terrible reason. Leviathan later fleshed them out a bit more, but Leviathan is not worth $10.
The lack of any real resolution is a pretty major point. Mass Effect 2's entire thing was basically getting to know and care about certain characters. And then that's just left abandoned. Nothing about the post-war period is mentioned at all.
The three endings were almost identical. Blue, red, green; there were small adjustments, but overall pretty much everything was the same no matter what you chose. And while red and blue were alright (although I felt blue had some pretty problems), green was just out of nowhere, and though it would appear that its supposed to be the "best" ending, it doesn't make any sense from any direction, not to mention the fact it ultimately doesn't solve any real problems. There was no sense of closure; the Crucible fired and then the credits rolled.
Then there's the kid. I
hated the kid. Not in the way I hated Kai Leng; I recognized I was supposed to hate Kai Leng and I went along with that gladly. But the intention was for me to care about the kid. I didn't care one bit. I did not like the game trying to force me to care about a character whose name I don't know, who appeared for less than five minutes, with the only reason given is because he's a child Shep couldn't save. The Reapers are invading; there's going to be a lot of people Shep cannot save. Not like there was anything that could have been done anyways; the kid got to the evacuation area and his shuttle was shot down. The recurring dream sequences focusing on the kid didn't endear him to me either. While I thought some of the dream bits were good, the fact that they centered around the kid and rather than the people I
had actually grown to care about over the previous game(s) annoyed me.
I
really hated the kid.