Sure there aren't that many cards but those cards are so well balanced. Every single card has its uses so you're constantly presented with interesting decisions. It feels like almost every other roguelike has dead time where you're just going through the motions whereas in slay the spire you're making decisions from floor 1.

I find there's a lot less variety in my monster train runs. Most classes have a distinctly best strategy and the artifacts generally also funnel you towards that strategy. For example, I can't remember the last time I played an Umbra run that didn't set up a morsel engine behind a warden or alloyed construct - as far as I'm concerned, those are the same strategy, it doesn't feel different. The only other build I think is viable is just "play Shadowsiege," which rarely happens early enough to build for it.

Every class in STS has at least three viable archetypes and almost every run within those archetypes still feels different to me.