Command is a fantastic spell. Except for one thing. It is language dependent. There's a rather large number of critters in the MM that don't speak common. It has come up so often that my current cleric often burns a spell on Tongues just to be sure to be able to use Command.
OTOH, the fact that command triggers on the opponents turn does make it an incredibly strong control spell and it scales very quickly too - 1 more target/spell level. Used properly, you can just devastate baddies with this. Especially brutal if you set up the rest of the group to take opportunity attacks as the baddie flees.
Heck, even things like "Drop" are brutal - you force the target to drop whatever they are holding and end their turn. The group gets an entire turn's worth of actions before that critter can pick up its weapon again. No opportunity attacks, and, if the group is smart, you can kick the weapon away as well.