Just finished playing it with my s/o. One run. It was The Run. We didn't even use a continue. Good feeling.
Enjoyed it overall! It got repetitive around the end of level 2, but in a way that captured Contra, so it only made it more "authentic". Actually the only bad thing I have to say about it is that stopping the action 8 times to build the decks is a pretty miserable experience. Even tho it would make more cutting work up front, I think I'd rather see each level / boss have its own complete deck that you assemble once and then just pick up and shuffle when you get to that level. Even as it is, there's more cards of certain encounters than any level / boss setup requires.
Other then that, we finished and think it's a game full of promise! It feels like it's just begging for a Castlevania expansion, or other other new encounters, power ups, and maybe ways to bring back that NES feeling of "getting better as you memorize".
Great job!