TBH the game was most enjoyable playing it single player. I've played it with 2, 3, and 4 players, and each one had a different frustration present.
With 4 people, everything is great, but even co-op becomes competitive with the ranking system. Everything gets explored quickly, however overworld areas can stretch thin at times.
With 3 people. "No I wanted Purple!", There is one extra guy and everyone wants to command him.
With 2 people, co-op is manageable and even fun, both players get to boss around 1 extra person. Fights do break out when everyone steals the other person's extra guy becoming a chain of 3.
Single player, Formations are king. You have full control of the team and can use various formations to their full potential. Nothing is more awesome than performing a hurricane spin while in diamond formation.
Most frustrating, 3 player
Most craziness, 4 player
Best co-op, 2 player
Least stress, 1 player
Four different ways to play, each a unique experience.