Well, Bioware have always been more action orientated than most RPG devs. So Mass Effect 2 was more like a perfection of what they've been striving to achieve since NWN 1 than a devolution to a more simplistic state.
I don't necessarily agree that action is a defining characteristic of an RPG. Naturally it is for most. But when it comes to the essence of what makes a roleplaying game a roleplaying game it quickly becomes obvious that you don't actually need any combat in the game at all. You only need the option to resort to violence. Not necessarily the motive for doing so.
That said, I certainly don't think you're wrong in what you say about the role you're taking on being an essential part of how battles are fought. It should be a defining factor. In fact, this is true of almost any game where you're not simply a faceless avatar.
Take another genre - Mirror's Edge as an example. Faith could run rings around most people. But using weapons was never her strong point. No matter how good at FPS you are, you had to play to her strengths more so than your own skills to survive.
So there are certain elements of roleplaying there. It's just that it's not a character you either created or have the ability to shape. The game ends with her having the same skills as those she began with. You don't develop her character one iota. So in RPG terms she's like a snapshot; a static state, and one that will quickly be surpassed.
In terms of interface, the biggest improvement is in its removal without stripping features and options out of the game. It's about making these things more streamlined and more closely tying together the various aspects of the game into a more cohesive whole.
In terms of Fallout 3, the improvements weren't t to be had in the console-orientated Pipboy. I liked the general idea. But it's implementation was far more clunky than it needed to be on PC.
The improvements came from the lack of transition between exploration and combat. The lack of dialogue interface (compared to Fallout). How these things were more naturally blended into one complete roleplaying experience.
Yes, yet more can still be done in these areas. I didn't like how people spontaneously talking to you forced you to verbally respond to them. Having the option to ignore them or even just get on with killing them should always have been an option.
Well, yes. Action RPGs are just action adventures that use RPG stats. But the line between them tends to get blurred. Mostly with games marketed as being RPGs winding up looking more like action RPGs when looked at more closely.
I'm not too sure about Mass Effect 2. It was very action-orientated. But then so are a lot of RPGs. The choices you made had a fairly clear effect on people and events. Especially if you imported an ME1 character. But character development was definitely very, very limited. Is it still roleplaying if you can't really shape the role you play? Not really. Not in my book. It's still a very bloody good game though.