The game balance looks good overall and the combining of cards is very interesting. Chapter 6 is quite hard though, and probably needs quite some card upgrades. And there lies a problem as the viagra for upgrades is hard to come by and requires quite some grinding.
Of course there are options when you spend money, and I would have bought them all as I enjoy playing. However epoch never seems to work for me. At least Smutstone has a fallback sales agent. I do look forward for them to fix this so I can buy all the upgrades.