Been playing Book of Demons:
it is a mix of card game and top down RPG. You have two cards stacks that you can switch between with the G button and you can for example have one for mana and the other for energy use cards.
You have a ladder down to the final boss and you can decide how long down you want to play by choosing if you want a game with less or more floors. So if you choose a 15 minute game, you would get two floors with a mini-boss or two and when you are finished you can continue down next floor or go back to town. You can also go back to town between each floor and replenish health/mana and the like.
The floors are tile bases, so you move along them and attack mobs by right clicking on your cards. You can swap them out and upgrade them and you'll be able to find even legendary upgrades to your cards or new card you find.
Some of the items you find go into a magic cauldron that gives you bonuses depending on how many items you save in it. So if you play good, you'll get extra rewards from it. You don't need to save them, but if you pick from the cauldron after each floor or game session, the price will increase for each time. Think of it as an extra reward that you can play with if you want to.
It's a fun game with increasing difficulty and I think the option to choose how long you want to play is a very good element to the game, especially for those who just want to jump in for a quick session. Progression is also saved, so you go back when you want.