I'm only 3 hours in, but from what I've XP'd so far this is gonna be one hell of a game, though I'm not sure if it's the sequel fans of the first will thoroughly enjoy.
Don't get me wrong, all the great things which made the original so awesome are still here... well almost all of them.
You'll be happy to know that the story starts off with a bang and does it's predecessor justice(I mean c'mon... Bioware). It's the gameplay which can go either forward or back depending on the gamer.
ME2 definately took a step forward for shooter fans with it's upgraded cover system. The A button is now the means for getting into/out of cover as well as redeeming it's role as the sprint and climb mechanism.
The weapon and special abilitiy venues remain the same, with an easier means for commanding your squad to use theirs.
This time around, instead of overheating your weapon of choice and waiting for it to cool down, there is an ammo system applied. At first I didn't like this notion, being so use to basically having infinite ammo, though it adds a level of tension for those moments when you really need to shoot a mother fucker or ten. Despite having been only 3 hours in, I've already XP'd moments where the enemy numbers are a little more than overwhelming compared to the first game.
Thus far it seems that you only level up when completing a mission as opposed to real time on the field action. I'm not 100%, but I don't even think you obtain XP the way you did in the first game. Something I'm definately missing. You also have to wait to be on the Normandy when wanting to change your armor, which is something you have complete control over how it looks. A cool little feature, but I do miss being pressured into wearing superior armor with the drawback that it's pink lol.
The change in the weapon swapping is also a bit disappointing. When you pick up a new weapon in the field, there's no way of changing it back to what might have been a more preferred sniper or pistol until you go to start a brand new mission. There's not even a stat gauge to compare the weapons you have. I've only acquired a 3 round burst battle rifle which immediately took the place of my standard issue assault rifle, and when I started my next mission I only had my XP with the weapons themselves as pref. This was what I was talking about, it kind of takes away the whole RPG style the original had.
Again, I'm not that far in, and I'm def enjoying myself because despite the things I miss, I'm still playing a true Mass Effect game. Will keep those interested posted.
FYI, you do have the option to import any completed game from the original Mass Effect, if you played and saved it. A friend at work asked if your level or personality(renegade/paragon) flowed over, no, you start fresh with everything. It's the big actions you took in the first game which flow over to affect this story. I'm anxious to see what else my previous actions have done.