Charming art style, great music, very silly writing. The only problem is that a roguelike/roguelite is mostly carried by its gameplay, and Going Under doesn't have those legs to stand on.
The combat never really evolves as you're frantically spamming the attack button every single run while scrounging for whatever has the highest damage. You don't get any invulnerability frames when dodging, nor can you use it to cancel animations so you're mostly committed to your attacks. Later on, combat gets so frantic and hectic that it's hard to tell what's happening and damage more or less becomes unavoidable.
You can pick a skill to start your run with but there's no reason not to choose the one that gives you five whole seconds of invulnerability. There are so many skills that completely dilute the item pool and unlike something like The Binding of Isaac, you don't have multiple pools to separate the skills from. Unfortunately, the skills you unlock earlier on tend to be much more helpful than the ones in the middle of the game, so you're just making it harder on yourself when you buy them.
When you hit the second part of the game, everything gets much harder without warning. All of the dungeons you were running before get enemies that are tankier and have attacks that are much harder to dodge. Thankfully you can hit a lever now to go back to the old dungeons but they don't properly prepare you for the end game.
I think this game is worth a shot on sale, but you shouldn't go in expecting something like Enter the Gungeon or Hades. It's a quick ten or so hour jaunt that's simple but fun.