Bah, I was doing a second play through of ME3 but I'm half tempted to do the trilogy again.
All three have their ups and downs. The first one probably has the best story, mainly because it's the great unknown.
There's what? 6 companions, 5 key semi-allies and 3 big bass to keep track of. There's maybe 6 core missions / locations everything else is primarily flavour.
1 of the core missions is filler anyway. After Eden prime and the Citadel you need to do 3 missions.
If you go to the Moon, pay special attention as that foreshadows the later games.