I'm three bosses in and it looks like a weird cross of Project Spark and Fable, and plays like the combat portion of Rocksteady's Batman games, but HoF is pretty fun so far.
I was expecting something more like Magic the Gathering, but - while there are deckbuilding elements - it's really just an action game with a random layout element to your fights. Put your deck together and that'll be the things you encounter during your run at whatever boss you're up against.
There are 12 bosses to go after, four rows of three on the board, and you can replay old ones whenever you want but have to beat the current 'top' one to face the next up the chain...and clearing each row grants you bonuses like better starting equipment, but also hinders you with things like buffing enemies.
Beat challenges/encounters and you earn tokens - those unlock new cards. Each boss has a card limit for your deck that you need to hit, so you'll have to add or subtract cards and that can make for some tough choices.
Beat the first row of bosses and I've gotten an artifact that adds (via the right bumper) a poison element to my blade for a short time - but it's slow to activate so adds some risk - and a frost blade that has a weapon ability...hit left bumper to do a cone of frost.
Put up a video of one encounter here:
https://www.youtube.com/watch?v=uDwm2dGfP9Y