We're a basically 100% unfamiliar with RPG systems (I know...) so this was a bit of a puzzle for us. I'll admit we didn't fully get it to the table because neither of us felt confident enough to take the role of a DM.
However, I think it's genius to create a system based on a standard deck of playing cards. Really takes the "what die do I use?" and "what's my modifier?" obfuscation out of it. Though it might be a bit of hurdle to apply different qualities to pairs of cards. As this is a work in progress, consider creating a clear player aid to make action selection as simple as possible.
The "rails" system of combat seems like it would add a different type of tactical interest to a fight that I don't think I've seen before. Questioning why a monster is taking an action in slot 8 as opposed to slot 5 feels unique and pretty dang cool.
It's not strictly co-op, but one versus many is co-op adjacent. ;)
I'm curious to know about the rest of the system. Does action selection such as spells, skill checks, and ... cantrips(?) work on a similar card-based system? Are those things included at all or is it a little more free-form? I applaud anyone looking to create a fresh RPG - it's a lot!
Cheers!
ps. Apologies if you got a bunch of notifications on this, my computer really wanted to send you this comment a million times.