Wow thanks for the very detailed feedback!
I definitely think this would be a run based game too, and you'd be able to die too (just not in the jam version as it's too easy).
Your point about progress plateauing and then having another layer appearing over the top is a really good point, I'll have to think about how that could apply here.
I'll have to check out Antimatter dimensions! Thanks for the recommendation.
I don't think this one would have offline progress, it's a game you have to play actively.
A bunch of different kinds of cards with different synergies is probably the way I'd go with it, and multiplayer is a cool idea - maybe if it's very successful down the line!
If you have any other thoughts I'm listening!