Couldn't agree more. Interactive storytelling at its best. Which is nothing new from Bioware
The campaign is long and rich, and the game has great replay value because of the different classes and story related choices available.
Couple of things I liked more in ME 1:
First of all, the main missions were more focused on the bigger storyline and there was more progression in it. The situation in the start of ME 2 is pretty much the same as in the end of it. It's more focused on introducing new characters. It may be harder to create a story for the middle part of a trilogy: the audience knows the hero and the environment, and the main "problem" of the story has been introduced already, but it's not yet time for closure.
Secondly, the more complex character development system + lots of equipment worked for me. I also liked when you were able to cast multiple spells at same time. Maybe I'm more of an RPG-ist than a shooter-guy.
But somehow the overall quality of ME 2 feels better. I think Speedbump summarized it well: ME1 is an RPG with shooter elements, ME2 is a shooter with RPG elements. Both are awesome.
It's a shame that Bioware decided to make their MMORPG based on Star Wars (The Old Republic), which has been completely sucked dry as a gaming franchise. "Mass Effect Online" would have been a thousand times more interesting.