A very poor attempt at a roguelike.
First of all: the content.
There's a minimal amount of it. 3 playable characters, 8 enemy types, bosses being just bigger enemies and all upgrades being purely stat boosts. Most unlocks you get for playing is just making the enemies a bit tougher sometimes.
Second of all: the difficulty.
The game is not hard at all. The game doesn't require much from the player. And the only difficulty is the growing scaling which the player can't really fight against easily since most upgrades you get during runs don't help you scale in any way. On the harder difficulties it gets very frustrating since the enemies get way too tough way too quickly while you get stuff like a 6% movement speed boost.
In summary, the game is just not good at all. Boring and uninspired all the way through.
Play Risk of Rain 2 instead.