This is going to sound completely insane, but Mass Effect 1's bad gameplay made the game stand out more to me.
ME2 and 3 had, objectively, better designed gameplay, but all they did was crib off every other third person shooter and then add in some sci-fi elements. All you are doing in those games is marching down hallways and ducking behind chest high walls, playing whack-a-mole with thugs and robots. ME1's fluid, sloppy, run and gun gameplay with pew pew lasers and overpowered biotics and vehicle sections that were smooth and intuitive as pushing a trolley down some jagged rocks made the game feel unique to me, and the level design was far, far superior, actually feeling like a galaxy inhabited by sentient beings rather than an endless supply of corridors.
I mean, in Mordin's recruitment mission, which takes place in a populated space station, the whole game zone is devoid of any signs of life. All you do is run around rustic brown zones. Or Thane's recruitment mission, which is set in a massive skyscraper run by a tyrant businesswoman in a glittering corporate city, which lacks any offices, restrooms, or even any goddamned desks. Just more chest high walls, even on the roof. Contrast that with, say, Noveria: You start out in a corporate-ran business facility, ride the Mako through a desolate, snow filled wasteland on your way to a laboratory, and then meet up with refugees, fighting Geth and Rachni through the laboratories, with no chest high walls in sight; you actually have to use your surroundings as cover. You don't just go from point A to point B killing everything in your way. You have to run around, talk to people, solve puzzles. Mass Effect 1 isn't perfect by any means, but I was simply so into the game's universe that I just didn't care.