Update: Okay, I spoke too soon about it being as good as Slay The Spire. I finally used all the heroes and I'm feeling like the balance gets screwy with all but two of them. Yes, it's cool to play this kind of game on an iPad, but ultimately it just makes me appreciate how well Slay The Spire nailed this genre.
I've played a lot of Slay The Spire, and I also caved and bought the IAP for Pirates Outlaws. Both are very similar, but sneaky IAP situation aside, I'd probably give the nod to Pirates Outlaws. I like the graphics better and playing on my iPad just feels better. That said, I initially left a scathing review of the game because of the IAP system which basically equates to: if you want to unlock the full game without tediously grinding for what I assume would be about 100 hours, it's gonna cost you roughly $20. That said, I think that's probably what I paid for Slay The Spire, and honestly, I found Pirates Outlaws more addictive (once I caved and paid the IAP.) Still, man was I ANGRY after I discovered that the IAP is structured in a way that paying anything less than $20 doesn't really fix the tedious grinding issue. So, yeah, I actually think this game IS worth $20, since when it opens up, I have to admit, begrudgingly, it's amazing.