The concept is really nice and simple to understand, especially thanks to the instructions.
The upgrades add a lot to the core gameplay, but I think it could use some balancing sometimes, especially concerning the card spawn speed (even after the upgrade), because I often didn't have anything to do and could only wait and hope for a good card.
I don't know if that's the case but it feels a bit like the game is sometimes trying to give us the card we want, but not fast enough (at one point I got a 5 when the timer displayed 4, a 3 when it displayed 2 and a 1 when it displayed 0).
I got a cool moment where I could do a combo and go from a 1 to a 9 and then place my 9! So I would have loved the opportunity for more cool moments, and be a bit more overwhelmed by cards.
I did have a lot of fun playing, great job to the team!