Games similar to Mass Effect 2?

which parts of it are you interested in? the witcher is very good, with skills progression, but in a fantasy environment. So you need to let us know what factors of the game you liked, and then we can figure it out better.

I'm playing Deus Ex: Human Revolution right now. It's pretty good, with voice acting and dialogue choices much like Mass Effect. The action is more stealthy than the typical Commander Shepherd run and gun, but the action is still pretty good. Good choices in skill advancement as you get upgrades. You can upgrade your weapons and use a bunch of high tech gadgets as well.

It's been on sale at Steam, you should check it out.