Enter The Review
I didn't buy Gungeon when it came out because it seemed lacking in content, but over the years it's received a number of updates that added a decent chunk of stuff. The variety of guns is insane, though they're locked behind a progression system that is kind of a slog. Each character has their own little backstory and the general theme of building a gun that can kill the past is interesting. Coop is really fun and you have a few ways to interact with the other player, like reviving them and swapping guns. While it doesn't have the replayability of something like Isaac, like most roguelikes it's more that worth the money you're paying.