I loved Mass Effect 1, but was somewhat disappointed in 2 for the following reasons:

I felt they were aiming at a younger age demographic and going for a more pure TPS, rather than a TPS/RPG hybrid. This is a matter of taste of course.
The game lacked narrative drive and got really bogged down in the side quests.
Too many squadmates with little to say, instead of a smaller number with more dialogue
The Collectors were lame, uninspired enemies who you hardly ever saw; it felt like your mission was to hunt down merc groups!
It also really annoyed me that I could not put my companions in proper armour or spacesuits for those times when, you know, they go into space!
No meaningful upgrades to your armour and no weapon upgrades to speak of.
No inventory or economy whatsoever!
Shrinking universe (a side quest mission allows you to eliminate the entire Geth threat from ME1!)
Planet scanning
N7 missions sucked; give me the Mako (with better controls) and those stunning vistas on unexplored worlds anytime

ME2 was still a good game with some really slick presentation with great voice acting (at times), and a few interesting characters, but it felt like the soul of the first game was sacrificed to create it. I think there was a lot of missed potential - the game would have been much more interesting if Cerberus had been shown to be undoubtedly evil and they had created a compelling reason for you to join them.

Having said all this; do you think I will like ME3?