Missions. Mass Effect is supposed to be an rpg, a shooter hybrid at that and ME1 did it well to some degree. Most thought the shooting mechanics sucked and it mostly did, though now with ME2, everyone are praising on how Bioware got it right. I might agree with that, because yes, the shooting mechanics are far superior than how they were in ME1, THOUGH where the **** is the rpg? Am I the only one who doesn't believe fancy (and flawed) cinematics with 'choices' makes a game an rpg? You need an inventory system, you need real choices with real consequences on gameplay - not just different ways to achieve the same thing, or one way to achieve nothing - you need quests and mini-quests (with interaction that goes with it) and you need the level design.
Like they say, one step forward two backwards. Like I said, the shooting mechanics are superior, but there's a lot of things with the big missions themselves which make ME2's mission inferior. First, yes I know, planets like Ilium and Omega have your standard RPG quests, but the moment you enter a mission, those quests or mini-quests are gone as most interaction except with some people at key moments. In fact, the missions are pretty much only standard third person shooter missions with some interactive cutscenes and different kind of classes available. Other than that, it's mostly corridors after corridors of shooting enemies, and of course, the whole area is disconnected from the rest of the planet, but anyway it's not like the area itself is particularly interesting. In ME1, the areas were designed intelligently as an "rpg area" for the lack of a better word. Look at Feros or Noveria for example, you drop on the planet do some quests or shooting, talk with some people about why you're here, some things you could do for them, find some crazy guy, shoot more enemies and it continues. You go from place to place shooting enemies and interacting with devices or people, the whole area feeling connected and giving you a sense of place immersion. I really think the shooting mechanics of ME2 should stay, but the missions of ME1 should come back, more connected and interesting missions should be made and fit with the rest of the planet.
Planets. Bigger ones, more quests please. Omega for example, really, it looks awesome and all but it's way too small. Take the Afterlife for example, it's only a couple of corridors really, you can't go anywhere but follow to the exit or some room or two, you can't go upstairs or anything, you feel like there's nothing to do.
Shepard/Conversations. Please, Shepard is a terrible character (even more in ME2), no depth at all, you have no choices. Yes, you can make choices on important things, but those things have no impact on gameplay, and those you made in ME1 are often only heard about in ME2 sadly. What I'm talking about, is the whole paragon/renegade thing. You either are paragon or renegade, and whatever way you choose, you always acquire or get the same thing, which is everything. Unless you try the grey road, which is loose-loose really, you always choose the same conversation options and get the same things, a paragon shouldn't get the same things as a renegade as people should react differently to both, one not getting intimidation and reacting to someone being super kind, add realism. Just look at KOTOR! You had tons of choices, from the biggest jerk ever to st. Peter saving the galaxy from the all consuming evil, you had CHOICES, you couldn't just get everything just by always using the top or bottom answers. Shepard is boring as he is either the biggest jerk or a super annoying saint.
Characters. More interactions, and interactions between them. In ME2 (while it was rather poor in ME1), it seems like your allies don't even know who is everyone else, it doesn't feel like you've got a crew at all.
Cinematics/Music. I loved the darker feel of ME2, but please bring back the more old school sci-fi elements of ME1 while keeping the darker tone. ME2 feels too much like those epic action-packed hollywood movies than the relatively "unique" feel of mystery and doom of ME1. Seriously, "we have to do this, do whatever it takes to save the galaxy" **** bores me to death. I really, really don't like this. Sure, it's about saving the galaxy or world like tons of games and RPGs, but it's how well the story is told and that element doesn't get too much light that makes the story better or not. Those big "saving the galaxy" moments trying to make you feel important, it really doesn't as I don't want to feel like a super hero, I want to feel like I'm playing in a special, unique and cool universe, and it feels like the story teller doesn't have that much of a compelling and interesting story if he resorts so often to those moments, those are really, really my biggest pet peeve in video games, well in any media telling stories. Saving the world is so overused, yet sometimes is essential to what you're trying to do and offers much at the same time, but the trick is to remind as little as possible the player that you're ultimately saving everyone. Just look at one of Halo 3's cinematics; "if Earth falls, every men, women and child are doomed", please! I almost cried because how of bad taste it was, and near the end it was pretty much like it in ME2.
That's the most important to me I can think of right now, but please Bioware, don't mess up such a cool universe and setting, I already think it's a shame both games didn't live up to their full potential. Oh, and can we get the real Therum for ME1 some day? Or under whatever name it was called as it looked so nice.