Rainbow Cult is a satirical office environment where each floor is based off a real-life event or controversy.
Gameplay
There are 13 basic enemy types, one is added every level you go up.

Even though it's single player, the combat often resembles an MMO more than any single-player genre, although it isn't grindy like an MMO. The way you pull and aggro enemies and use crowd control to avoid damage should feel familiar, but RainbowCult ratchets up the pace much higher.

You can throw three basic spells, but these also can be combined in six different ways to make important utility spells that add a lot of variety to the gameplay.
Bosses
The boss fights could be described as a puzzle, much in the same way that MMO boss fights are a puzzle - you have a limited set of mechanics and you have to figure out how to apply them to the encounter.

These 13 bosses each have 3 difficulty levels, which add new mechanics to the boss to make the fight more dynamic and challenging, training you for the final NG++ encounter. There aren't quick-time-events or glowing weak spots. Just you, a handful of spells, and your wits.

Can't figure out one of the boss fights? Skip it and come back later when you realize what you were doing wrong!
Multiple endings
Each of the three difficulties has a unique cutscene at the end, rewarding you for beating all 13 of the bosses.