1. Abolish mining for rescources. Have the player gather whatever they need over the course of the game. (Doing side-quests and the like)
2. Better side-quests. I think this speaks for itself.
3. Bigger missions. ME1 had fewer, longer missions. I liked those. ME2 has more, shorter missions. I enjoyed some of them, but the ones in ME1 were just more epic. So they should find a middle ground between the two.
4. Stop making me walk all around the ship just to talk to people. Can't I call them into my office or something? That would make things a lot easier, though maybe that's the point.
5. Sure, bring back some RPG elements. Personally, I don't really mind the dumbing-down of ME2, but I wouldn't mind it being a little more complex. As long as the inventory isn't as cluttered as ME1, I'll be happy.
6. More discernible villain. Saren=Good. Sovereign=Good. Collectors=Bad.(It's hard to have a personal hatred for an entire race) Harbinger=Bad. Except for his eargasmic voice. (It's hard to fear or hate someone you routinely set on fire and kill. Especially when all he does is lob generic threats at you.)
7. Don't make me go full-renegade or full-paragon in order to win.(i.e, get my entire crew out alive. Morality should not be black and white.)
8. Elcor or Hanar crew member. I don't care how, just make it happen.