1- The missions are mostly very similar but the combat is much more satisfying and smoother than ME 1- the increase in weapons, squad members and biotic powers available to use help keep it fresh. It hasn't felt repetitive to me at all.
2- I've put 25 hours into the game (finished the first in 24 hours) and my guess is that I have another 7 hours ahead. I've been doing all side missions and landing on every planet in the game so it feels long to me.
3- Eh, true.
The Meta score is spot on, imo.