I don't even know if I'd agree with the common sentiment that only the ending sucks and all the 30 hours before it are amazazing.
I didn't like most of the story and mechanical elements that ME3 brought to the table.
Story:
- Crucible + Catalyst: They constantly stress the scale and importance of the project but don't provide the setup or context necessary to appreciate it as such, which ultimately unmasks it as the shallow deus ex machina inserted by the writers it really is.
- Kai Leng: Terrible character. ME's version of Jar-Jar Binks. Annoying and out of place.
- The Illusive Man: Completely forgotten for a large part of the story after being so integral in ME2, suddenly appearing at the end only to be thrown aside 5 minutes later. What a waste of a potentially interesting villain.
- Shepard's reaction to the kid and the dreams: These hokey attempts at characterisation caused a pretty heavy disconnect with "my" Shepard. My renegade Shep is a colonist dick and doesn't give a shit about either that kid, or earth for that matter. ME3 seems more like Bioware's Shepard than previous games which is probably the biggest offense of them all.
Mechanics:
- War Assets: reducing pretty much all of your choices to numbers in a green progress bar. What a terrific way to reduce and dampen the impact of pretty much every potentially interesting choice made in the game. Was thrilled to find Zaaed in my game (one of my favourite ME2 characters) only to have him disappear into my progress bar as a "25". What shit.
- Benny Hill Reaper Chase on the Galaxy Map: Pretty silly, inoffensive (since it's easily circumvented), but you do have to wonder why they thought this would add to the experience at all. Similarly misdirected as adding tower defence to Assassin's Creed.
- Scanning minigame redux: WHY!? Well, it's better than in ME2 (so is jabbing needles into my dick though), but still a meaningless and ultimately boring time-waster. Made even worse due to the lack of feedback in some star systems, was ting even more time.
Nitpicking aside, ME3 feeds off the setups in the first two games, runs with some and squanders others. Provides the strongest shooting mechanics but the most shallow/limited roleplaying mechanics in the series.
High production values ensure that I can't really call it a bad game and I still liked my time with it, but it's definitely one of these cases where the longer you think about it, the worse all the small problems get and add up.