Achievements are minor spoilers, so click at your own risk!
Mass Effect 3 Achievements It's nice to note that there's no achievement that can be unlocked by multiplayer only, so people worried about that can rest at ease. There's the option for MP or SP ways to unlock achievements, so you won't feel forced to play MP mode.
For example:
Tourist: Complete one multiplayer match or two N7 missions.
Glad they went this route!