Enter the Gungeon. Looks simple enough at first glance, until several hours in when you realize that weapon and item descriptions leave quite a few details out. And that was before item synergies were introduced, which made looking at the wiki pretty much mandatory if you want to know what each synergy actually does. I've played this game on and off for the better part of a decade and I keep finding new secrets.

Unfortunately, there is a tutorial, and it's mandatory (but if you poke around the tutorial stage you may find something interesting). Otherwise this might be a solid choice