Mass Effect 2 - Preview @ IGN

According to Greg Zeschuk in this IGN preview of Mass Effect 2, this second game is intended to be "the trilogy's Empire Strikes Back", being darker and harder:

Combat has dramatically improved in ME2. As soon as you get it in your hands and begin running for cover before snapping up your sights on oncoming enemies, you forget that you are even playing an RPG. It's all so fluid. "Well combat was one of our big focuses. The original was the first time we had ever really tried a shooter, and just getting the game done was a lot of work. So as time has rolled on we've just got a lot better at doing the combat. The tradition of the RPG is a lot more like Dragon Age, whereas Mass Effect is more like a game with RPG features. I would consider it more of a Shooter RPG. Especially after the changes we have made in this one: it is even more like a shooter. It's very doable to make such a mix work; you just need to get practice with it."