Having played this a little bit more to finish it...
All the modes are too short. It feels like you're being told "no fun allowed" whenever you're just getting your build going. And I can barely feel the difference in their difficulty.
Red is junk.
Black is grotesquely overpowered. Inactive turns are extremely common and not the imposed limitation the effects seem to assume. The dog being busted as a final unlock makes sense, but the samurai, not so much.
Wildcards are disproportionately good, but they add so much player agency to the game that I would like to see even more of them.
Yellow, besides the extra interest one, is awful, but that's mostly because the runs are too short. I think it might be actually impossible to get any value out of the briefcase unless you pick it exactly on the final round of the run, considering the lost interest, and even then, it's barely a payoff. Color buffs are often not worth it even if you're mono-color (and there's no reason not to be.) The high rarity items are all overpriced junk, so why would I want more of that? The only time I mathematically got any use of any was in using the cheaper rerolls to get the fully upgraded build badge.
Weapons are very rare to come by now, yet upgrading them is such a big advantage. Are you going to have more weapons besides the starting ones?