This has become one of my favorite games of the year. I started by playing the free mobile version that gives you a shorter maximum campaign, (12 battles as opposed to 20) but was drawn in quickly to purchase the full version. (No ads in either, 8.99 on the IOS app store)
It looks like this is on steam too, and I might consider getting it given the UI can get cluttered in some of the custom modes that have a lot going on. But it is the perfect type of mobile game to me, so I don't know if it would have the same draw to me when sitting in front of my computer.
Gameplay is simple: you have a party of 5 characters whose abilities are on the six faces of the dice. You play Yahtzee style battles. The enemies roll their abilities first, so you can see what they will do and who they will target. Then you get to roll your characters, locking in those you like, and re-rolling up to two more times for those you do not. Then you get to perform your actions with as many undos as you need until you confirm ending your turn. At that point, the enemy will proceed as planned. You repeat this process until all enemies are defeated or until your remaining HP is over a certain percent higher than the remaining enemies, at which point you can let them flee.
After battles, you will always be presented with the choice to level up a hero (more HP, more complex abilities, usually less empty sides of the dice) or a few items to equip that modify something about the character. After odd battles you will level up, after even you will get items. Additional choices will occasionally pop up as well.
As you play and complete various tasks, you will unlock more features of the game. It is a very natural progression that only increases the things that can be modified and the crazy strategies you can potentially employ.
I highly recommend this game! It suspends battles so you can easily pick up and put down for short sessions, or play for hours on end. Get the free version, and play through the first two or three difficulties. By then you will definitely know if it is for you!