The Mako sequences would've been better with more intuitive controls, better suspension on the buggy itself, and variable gravity fields. The codex goes to so much trouble including the surface gravity of each planet, it would've been nice to actually experience in the game itself.
But my major #1 request of ME2: BETTER LOAD TIMES!!! *pant, wheeze* I can't tell you how much it annoyed me, having to sit through that tedious elevator ride every time I wanted to chat up and eventually nail Ashley.