I rented mass effect 1 for an hour and didn't like it, but I picked up Mass Effect 2 after everyone and their dog telling me that action has been greatly improved. I spent about 14 hours with Mass Effect 2 thus far and while it is an improved experience for the action junkie, I find it still somewhat lacking.
It seems to me like Bioware must not have played Contra, Doom, Quake, Vectorman or any classic twitch action game as they have no clue how to generate tension in their action set pieces. Furthermore, the set pieces are 1/10th as imaginative as the best stuff found in some other games. Remember the last level of Half Life 2 Episode 2...with the tripods coming and defending the base etc. Well there isn't anything as engaging and tense in Mass Effect 2...not even close.
It almost looks like they miss the chances to make action gameplay more intense on purpose too. One of the missions involves traveling to a planet to help Zaid sort out some old grudge with an ex partner. There you find an option to save workers stuck in a burning factory complex. This situation would be 10X more fun, if it actually had a timer before factory explodes. that way you'd have to hurry up and shoot fast and quickly figure out where to go and what to do. Instead you get to strol through the burning factory without a care in the world...shooting enemies at leasure, powering up your weapons...etc.
I am not saying the game is not good as it clearly is an amazing package. I just wish the action elements were better...as they have no reason not to be.