Finished the game at about 26 hours and change, didn't do more than 2 side missions, but I did all the loyalty missions, her's what I think of the game.
Some of the best dialogue you'll find in any game.
Great side characters and good character development through the adventure.
Much improved combat and space navigation over the first game.
Good music (like the first ME) and the voice acting is almost universally good.
Liked the higher number of crew members over the first game and I enjoyed the loyalty missions that gave depth to the characters.
Side missions and loyalty missions are way better than what you could do outside of the main story in the first game.
Good build up at the end, I liked how different characters' lives were in danger at different times and it created tension.
Less glitches and a better frame rate than the first game.
Still not as good a 3rd person shooter as Gears of War or Uncharted 2 (which is a minor complaint in a game this big).
Wanted additional new alien races to be introduced.
Still a relatively empty galaxy, even though it is much better handled than the first.
Weak final boss compared to the rest of the last area.
The ending theme is nowhere near as good as the one from the frist Mass Effect.
The only major complaint I have is the amount and length of loading times, people complained about the slow elevators in the first game, but at least the other two members used to talk to each other while you were on them and watching 3 people go down on an elevator is better than a load screen.
The human characters were a lot better than Alenko and Ashley from the first game and almost all the characters were great (Grunt was a lesser Wrex and Legion was unnecessary). At the end, I didn't let Cerberus keep the ship and I went all the way with Tali (thinking that I'd see what the Quarians look like under the suit, at least their faces, but was disappointed by that not happening).
One more thing, this is the only game that I probably spent as much time talking to people as I did fighting or killing them.