Having just finished Mass Effect 3 and finally being able to read articles about the ongoing debate regarding its ending, I feel like I'm going to have to side with the disappointed. Mind you, this isn't a Battlestar Galactica level of disappointment, where the final episode (primarily the last few minutes) ruined the series for me retroactively. With Mass Effect 3 it's more a mild disappointment in the setup, delivery, and execution of the game's final choice. The game basically presents the player with 3 options that (while all valid) left me wanting to argue for a 4th choice. The reason I believe there should have been a 4th choice is because I spent a good portion of the game proving that such a solution could work.
Anyway, the game (and series) as a whole is AMAZING. It moved me in ways no game has ever moved me before. As far as the ending goes though, it leaves something to be desired for those who followed what I believe is a prominent narrative path through the series. I'll get into more detail at a later point though and that post WILL contain spoilers.