You do have an extent of control over your creatures, starting with the fact that you can fully customize their ability loadout. Also, there's the star system which influences not only the damage they deal and take, but also their behaviour to a degree.

Some creatures are really powerful. Goon learns the Elixir and Phoenix Down abilities, Chocobo learns Auto-Haste and Meteor, Elementals tend to learn 1 MP Cost and have very good defensive stats (except for HP). Give a Large creature the White Mage dressphere and they're incredibly durable.

IMO one of the main selling points of Creature Create are the fiend tales. Every creature except for a few (and all NPCs) have their unique little storylines, since they used to be human. Sometimes these are very nice, ranging from funny to feelsy.

Plus, the Fiend Arena is all sorts of great.