As for the comparison with Bioshock 2, there are also plenty of choices to make in Mass Effect that affect the way you play.
- The team mates that you take with you
- The weapons configuration that you take with you
- The upgrades you buy
- How you upgrade your powers and those of your team mates
- Doing the loyalty missions of your team mates, unlocking a new power for them
I know this is pointless and should just shutup, but for some reason , I keep feeling I need to make myself clear. I have taken all of these things into consideration and am not ignoring them. I simply feel one can argue effectively that for the most part, there is not much difference between these two games in any of these respects.
I played at at the harder difficulty levels, and I can't see how the selection of teammates made a material effect on gameplay, still basically a shooter and the experience was still basically the same. Maybe, one could argue that it may make it a tactical shooter, but not exactly a hardcore one. Not really sure what this has do with making it more of rpg regardless.
As far as the other things you mentioned, everyone who plays the game gets exactly the same thing and gets the same experience. Weapon loadouts don't matter, as you simply pick the best weapon you can carry in each class. Everyone gets the same upgrades if they click on every obvious interactive point and grinds the mining minigame. Only things that differ are class weapon restrictions and which heavy weapon you choose. You can switch loadouts to much more meaningful effect in BS2 and also need to choose which weapon upgrades to get and when. So don't get how this makes it more meaningful a choice in ME2.
Sure you get to select which powers to upgrade, but everyone gets all powers and eventually maxes them, with only gradual increase in effectiveness along the way. Same thing with team mates, but to an even lesser degree. Everyone completes loyalty missions (as these are at least 1/3 of the gameplay) so those powers are given. You do get to select a unique power, but its either a passive one or an active one that shares a cooldown timer with others. So it is still largely, hide, shoot, activate power x, hide shoot, shoot, shoot. Sure you can throw in a tell companion a to hide, shoot from here and occasionally activate power x, but IMO its still just a shooter and character/team development choices don't really have a material affect on gameplay.
Can you realistically say, that you are going to play ME2 through again? Do you really expect that the game will be that much of a different experience, if you do? I have no desire to replay Bioshock 2 after finishing it for the same reason I have no desire to replay ME2. It was a fun shooter with a good story, but the experience isn't really going to change next time through, regardless of which "choices" I make.