STS is a fantastic baseline but I can't help but feel they dropped the ball in the content department. The tower and amount of enemies feel way too limited
Ah, but the genius of STS is that actually works in the game's favor. With enough experience playing STS and metagame knowledge you start being able to make more informed decisions on card selection/path choice/relic and adventure choices based on your current deck and position in the game. With a wider pool of enemies/encounters/bosses that dilutes the decision-making when you're deckbuilding and picking relics, whereas with things more focused you can start thinking "Fuck, I'm headed into act 2 I really need some good AoE because act 2's full of group encounters" and "Oh shit I might not want this card because if my act 3 boss is This Dude that'll fuck me". More differences in the classes are fine since those are swapped in and out whole-cloth and you can adjust your strategies accordingly, but the enemies are the framework that you play everything off of.
Plus this isn't really an answer in itself but if you do want more variety in StS then I heartily recommend checking out the workshop. There are a bunch, A BUNCH, of really good expansions/addons for StS, and you can run many at once if you're so inclined. Specifically this one is probably the best general expansion of existing content, but there are new/alternate act mods, a bunch of new classes, etc.
https://steamcommunity.com/sharedfiles/filedetails/?id=1610173938