The worst part - and it is a mechanic I especially loathe - is that like most hero collectors you can level your units up, but this kills any PvP strategy whatsoever. It means that I can send a knight against your knight and get wiped out because you’ve simply grinded longer. I can’t tell you how much I detest that. I’d rather the game reward grinding with more powerful units so that you then at least know what you are up against. It is simply inherently unfun and kills most of my desire to even play.
All that said, Rumble does appear to have a fairly large campaign system, so there might be legs there if anyone is actually interested.