I want to start by saying I loved this game, I loved it so much I'm replaying it, but years of loving failed franchises has honed by ability to tune out the bad and enjoy the good. All my future playthroughs are probably going to see me turning off the game five minutes early. So I'm going to split this into two bits, things I'd like to see tweaked/added in the bulk of the game, and my feelings on the ending.
MAIN GAME
* The shooting range is an excellent touch, but I'd really like to be able to use it without hauling my ass over to the citadel. Isn't there enough room in the shuttle bay for a range? It'd be a fitting addition for the Normandy, I think.
* Relatedly, I'd love to see numerical data on the guns in game. Their stat bars are sometimes misleading or hard to judge, and things like damage multipliers vs various defenses are impossible to accurately pin down without frustating testing, when they could easily be displayed in plain text. It might be a bit immersion breaking for some, but hide it behind a button and it should be fine.
* It'd have been nice for the romances to have a bit more flexibility based on if you picked up a thread from past games. My Shepard has been true to Liara from ME1, and from the first dream sequence on there were plenty of times when it just seemed like Shepard or Liara needed at least a hug, but they were locked in a romantic holding pattern so things could develop naturally for new players. My impression is Liara's was the best romance in this regard, so I feel bad for other Shepards(Lovers of Jacob in particular.) This would have been a lot of new content, but so long as I'm dreaming... I did very much enjoy the romance plot and all the character writing in general.
* Why are all the galaxy's ships still using mass drivers as their sole prime armament? The Thanix Cannons are demonstrably devastating in ME2's ending, and while it's entirely plausible that only some ships would be refitted with them by now, it's boggling to think none of them are. This question is present through all the battle scenes in the game.
* I'd have loved there to be basic husk varieties of all aliens, possibly as far as making Husk, Cannibal, and Marauder to be 'classes' of husk that can be applied to all species. This is most aggravating with Krogans and Asari; we're told that only Ardat-Yakshi can be Banshees, and they compose a tiny fraction of the Asari population, so what are the reapers doing with all the other Asari? Brutes on the other hand are just a goofy idea. They take husks from sufficiently advanced technology to just plain lego genetics, if the Reapers can glue species of different amino acid chirallity together like that, I find it hard to believe they need any stock to work from at all. Were mutant armored berserk krogans just not scary enough on their own? Again, this could be content prohibitive, but would make the situation feel more real to me.
* Better quest tracking would be nice. At one point I got a quest to help evacuate the Elcor homeworld, but then found that I didn't know what system or cluster it was in. I was thus entirely unable to find them and do any good. This problem plauges all the quest tracking.
* I really wish we'd seen suitless quarrians, and I wish if we had seen them that they were decidedly nonhuman in face. The Asari looking so human is frustrating enough from the perspective of a hard sci-fi lover, another set of human faces in the universe would simply compound the issue.
* I wish my alien crew didn't wear armor everywhere. Shepard and James both have casual wear, I'd rather see Liara wear that old Asari Scientist outfit, Garrus get on those funky Turian clothes, maybe have Tali hang up some of her gear for a while(though obviously not desuit totally). And if I were in Shepard's place, I'd have found a spare uniform for EDI before letting her wander the halls. I know she's a robot, but c'mon.
SUBHEADING: Multiplayer
* I'd LOVE some MP game modes that deviate from the hold-against-waves formula. Pushing through fixed enemy defenses would be wonderful.
* Face customization would be nice. Separate facepaint color and pattern for turrians and asari, stronger skin color options for all... Shepard levels of face customization would be lovely, but super unlikely. Same with armor piece customization on humans/everyone. Maybe a few different outfits?
* A variation on the Spectre shooting range would be appreciated. A testing mode with some targets, no AIs, and a weapon bench. Let me test out weapon loadouts, cooldown times, and my interaction with my teammate's cooldowns. Probably relatively tricky to code, but it'd be a godsend.
ENDING
Logic/Lore/Plot: Though I feel dirty for saying it, this is the category that means the least to me. It's important sure, but I was prepared for plot holes galore and I think I could live with them if the ending was otherwise satisfying. So I'll skim.
* The Catalyst AI, how does it exist but have no influence over the Reapers? This is a pretty big deal, because the whole point of ME1 was that the reaper's automation of the citadel was broken. Now there is a Reaper related AI on the citadel? For that matter, why didn't the Reapers turn off the mass relay network once they had the citadel?
* The Catalyst asserts that the cycle of AI overthrowing organics is unavoidable and implies that it has happened many times. If this is true, and without any destabilizing influences from past cycles this is unavoidable, then who build the Reapers? It can't have been the galaxy's first organic civilization, since their AIs must have overthrown them. Could it have been the first cycle's AIs? Why would they set out to preserve organics after having exterminated theirs? It can't have been the second cycle's organics, because there wouldn't be any, the first AIs would have total galactic dominance and not allow such a challenge. Unless something wiped out the first AIs, in which case the cycle existed before the reapers and there is no need for them to exist. Other working explanations for Reaper origins and behavior are possible that have fewer holes than this, but if anything was going to be left mysterious as this series closed, the motivations and origins of the Reapers should have been it.
* Theres that Conduit thing on Ilos that seems like it'd let us bypass this whole mad dash through London business. This could be written around any number of ways, but should have been at least mentioned, possibly only mentioned if you imported a save with ME1 data to not confuse new players.
Theme: The ending of ME3 seems to be built on the premise that the theme of the series is Synthetics vs Organics, but that doesn't seem to be the case for me. In fact ME3 actively undermines this ending. EDI is develops towards humanity the whole game if you lead her down that path. The Geth form a symbiosis with the Quarians, if you help them. Then in the end, your choices revolve around the idea that everything you just did isn't possible.
Looking back on the series, I think the theme running through it that speaks strongest to me is one of personal agency. Player choice is central to the experience, but also shepard's choices, and Shepard's defiance. The council tells you you're grounded, that theres no such thing as Reapers, and you steal the Normandy. Everyone tells you Cerberus is bad news, or that the Omega 4 relay is a suicide mission, but you fight the collectors anyway. The Illusive Man tries to control you, and you tell walk off with the SR2. Can't cure the genophage? I cured it. Can't unite the Quarrians and Geth? I united them.
So in the end, you have player choice yes. One choice that renders all your history pointless, not a culmination of past decisions leading to one inevitable conclusion. No matter what I've done, so long as I've scrounged the galaxy enough and played enough MP, I can switch courses at the end and anybody else could do the same. And It's not a choice of Shepard's making. Shepard is handed the ending, as if god came down and said "Yes, you did well Shepard, now die and I'll make everything right." There is no final heroic sacrifice, Shepard instead rolls over and lets someone else do the thinking in the final moments. This is why the ending feels like it's a betrayal of her character to me, because it doesn't grow naturally from what came before, but instead happens because the narrative demands a resolution and a death.
Emotion: The run through London may not have been the most tactically/loreisticly sound battle sequence, but it got my blood pumping. I got into it, I shouted at the reaper destroyer, I shouted in victory when the missiles hit it, I swore at harbinger. I was excited. Then the beam hit me. When I got up, my first thought was 'where is my squad?'. As I stepped into the beam I wondered abut Kaiden and Liara, worried if they survived. Walking through the citadel, talking to TIM, talking to the Catalyst, all throughout I was /distracted/, not excited.
Talking to TIM I started to get back into it, because that was very well written. I believed that this man believed, and that he was dominated, I bought the story again. But the conversation with the Catalyst, the final moments... I didn't feel victorious, I felt helpless. I threw myself into the green ending because I felt it was the only option available to me, it was a form of desperation. And the final scenes? The Normandy flying away for no good reason, Liara back on the ship for no good reason? I was confused.
In the end I felt drained, and not the least bit triumphant. Drained is to be expected, at the end of a powerful series you should feel exhausted by all the ups and downs. And don't get me wrong, the ending shouldn't necessarily be all roses, it should have some bitterness. This is a war, and the game goes to considerable length to tell us that war sucks. But Mordin's death scene left me feeling sad, but like he went out well. Like that was the only way he could have gone out. Shepard's death was just... empty.
Why? Because through the whole game it is built up what we are fighting for. The game got me into Shepard's head, I think. I didn't want to beat the reapers to beat the reapers. I wasn't fighting to beat the reapers. I was fighting for Earth, for Palaven, for Thessia, for Tuchanka and Rannoch. I was fighting to save all the people I'd come to know over these three games, to give them the chance to rebuild and make right the damage. None of the endings gave me that. While I do want to see my Shepard in a seaside cottage on Rannoch surrounded by little blue children, Normandy and Mako parked outside, I'm not going to pretend that's the only ending that would satisfy me. But this sudden death... the ending brought me to an emotional high and the just ended, as sure as if I finished off TIM and then got a screen saying "Game Over, you win!".
BACKSEAT WORLDBUILDING
I had a few ideas on how I'd have written certain elements without going entirely off the rails of the game as it exists, and felt like sharing them.
* A conventional victory: The Cruicible is a giant disruptor bomb. Hook it up to the Citadel, turn it on, and it rattles anything in range with an active mass effect field into paste, Reapers inlcuded.
* Repear Origins: The first post-singularity civilization in the galaxy, eventually coallesed into the first Repear and left the galaxy to ponder infinity in dark space. They return every so often to bring other species up to Reaperhood in a way that enhances their(The reapers, that is) collective existence, ensures loyalty, and prevents any species from reaching a similar level of existance while still retaining any free will and thus being a threat.