1. Bioware said that they didnt want to introduce as many characters as they did in ME 2, which was lot (and 2 junk DLC characters if you ask me). Therefore they focused on a few characters from the past games, which was fine then added two new garbage characters to the game. Honestly, James was lame, would've spaced him out of my ship in a heartbeat. And then that new female character, based on a game journalist? Refused to even pick her up. A great waste of resources creating these two uninteresting characters, for what? And then they added a so-so DLC character for 10 bucks, yipee! Keep lining your coffers Bioware.
2. You worked so hard to keep everyone on your team alive in ME 2 (well at least I did) and then watch a few of them die one by one in this game (I mean Legion? Really? he was one of the best characters of all time, IMO). I understand everyone must sacrifice for the war, but it just seems kind of contradictory.
3. Dialogue between you and your teem was drastically reduced, to the point were it was like the non existent dialogue with the ME 2 DLC characters. Another stripping away of the already fading RPG elements of the series. Also, talking about RPG, I thought the progression system was pretty similar to ME 2, still way watered down from ME 1.
4. Adding the online component is kind of lame, kind of forcing single players to play multi to get the best outcome.
5. The endings were god awful. It's not even the fact that Shepherd dies (although that should be reserved for a poor/renegade playthrough). The entire series had epic momentum to it, you felt like you were right there and filled with electricity, compelled to play for hours on end, and your emotions were roused (like when you destroyed the collector base, man I got goosebumps!). This game had this too, and leads you to expect something epic is coming in the end. However, the conclusion was a massive let down. The entire time your trying to gather forces, and to create a weapon that can defeat the reapers once and for all. This is awesome, until the last ten or so minutes of the game, when you meet this child-like thing that I guess is the sum of the reapers. I don't get what they were thinking! The choices you have to make totally disregard any decisions or actions that you made in previous games, and all of them suck (oops). There is no good ending, even if you get the clip where you see (maybe) Shepherd breathing in the end. The end killed this game for me, made me feel like everything that I had worked for in the past 2 games was all for naught. I think the writers made a terrible decision to make this the conclusion of the trilogy, because instead of making you want more, like the past games, this one makes me want to steer clear of EA and Bioware games...
Below is how I think the game should have ended on a paragon playthrough: The Crucible is a weapon and is a massive EMP that sends out waves throughout the galaxy, destroying the Reapers, the galaxy is saved and Shepherd either lives, dies unleashing the weapon, or is transported to an unknown location (like what happened to the master chief at the end of the halo series), or something along those lines. As it stands I would say, sadly, stay away from this title. I thoroughly enjoyed the majority of this game, lost hours of my life that I will never get back, and now I wish I never had played it, or even the series because of how devastatingly moronic the ending was... Kudos Bioware, and thanks a bunch EA, you killed a great game and an almost epic trilogy, thanks.