Final Fantasy Record Keeper is considered to be "what ATB should have been in the first place", with a similar set-up and draw (form a party of Final Fantasy heroes, explore levels from their home worlds) but a much more complex gameplay system with much gentler micro-transactions.
Though it's still not highly regarded, people began to warm up to the game a bit more once it was made free to download. At that point the only things you need to pay for are optional extras, you're free to ignore them and just play the base game, which is nothing special but provide an adequately entertaining way to waste time.
The battle system. Just swipe your finger/stylus over your characters like mad, and you have a system. That's it.
Having to pay for new areas and new characters is a dick move, but excusable since they are optional extras. What isn't is that the gold hourglasses you need to revive the party cost money. Yes, when your party is getting pummeled, your only options are to wait three minutes of real time as they revive automatically, or pay money to revive them instantly. You have to pay more money to revive your party members.
They Changed It, Now It Sucks: The main accusations that reviewers like IGN and Game Informer make whenever the game and its battle system is brought up.
They Wasted a Perfectly Good Plot: Based on premise alone the game could have been great, and the sprite work is awesome and shows there was real effort put in. The result has not only been underwhelming, but completely hated by fans and reviewers alike. Square Enix themselves seemed to recognize this, as the premise was basically recycled into Record Keeper, which has done far better.