Too much changes lead to unsatisfied experiences.
Beginning with unnecessary changes such as weapons and armors.
All the weapons in ME1 requires energy to shoots and is balanced by overheat. Why do we need ammo all of a sudden? where are those weapon that doesn't need ammo? I understand they are forcing us to balance our gameplay by mixing in some biotic or tech moves by unfortunately i feel the game is not well tied with the previous one.
I cant equip weapon of my choice, nor armor. I am stuck with 2 pistols and a heavy weapon (Sentinel option), and later i can choose between, shotgun, sniper, and assault rifle. Heck I miss the old time where i can equip whatever i want depends on the situation, now i feel restricted. (Assault rifle and sniper rifle was my favorite combo, now I can't use this combo.)
Armor is no longer a choice, I guess they are lazy on making more skins for those, instead they made some casual outfit for Shepard. There aren't really a value for armor anymore, really strange.
Power wheels is gone on the pc version, not sure about the xbox 360 version but I can use 1-8 to control my power which makes this game much faster in paces and much much less time spend in the wheels to move your partners around.
Regenerating health is also a big mistake, I want my armor and health value back please, regenerating health and shield are totally making the battle easier. The health pickup is more use for reviving than healing. Most of the time I have more to spare because I can take out all the enemies and let my sidekick revive automatically.
Last thing I can say that really kept me disappointed was the side missions. Other than character specific and main quests I never touch them. It clocks me around 20 hours as I finish the game, short short short game in my opinion. I can conclude by adding another replay and that is it for this game. Most of the assignment or side quest is completely chores. Come on people we got the galaxy to save, don't send me to scan stuff again!!
However I do like some of the new stuff they put in, including the planet scanning, which is more fun to do than actually go on the planet and look for stuff. I got all the resources I need for upgrades before I got bored of it. Hint, only visit rich resources planet.
Overall, when the game ends, I feel like there should be more, the story didn't really leap forwards by a lot but certainly it advanced forward. Old characters (especially the "can be dead" one) are moving on to their own path, some old characters returns *shocks* and new characters joins, a major battle ends ME2 leaving the reapers still being our major threat and the final showdown comes in Mass Effect 3. Until then.