It's tough to rate a movie like "Ostermontag", because it basically does what it says on the tin. It's not meant to be clever, coherent or even entertaining. It's supposed to be disturbing, and it is. Writer/Director Heiko Fipper has created a very nasty experience. While most of the movie is tolerable because of the cheap effects and subpar acting, the ending scene is genuinely one of the most 'authentic' and nauseating things I've ever watched. It's almost like Fipper intentionally make the rest of his movie look fake just to shock us more with the ending. If so, well done I guess!
With that said, obviously this is a really bad movie. Most viewers don't understand the plot because you can only get this in German. I speak German and still don't understand much of the plot. It doesn't help that some characters look pretty similar, particularly when filmed with a toaster. In other words: for most of the time, I don't know who's doing what and why. To add insult to injury, the movie is very slow and most scenes go on for way too long. If you have this much filler and still only clock in at 64 minutes, you should probably write more.
Heiko Fipper only made one other movie. "Das komabrutale Duell" has a more comedic undertone and looks more like a lost Andreas Schnaas movie. "Ostermontag" is a much nastier watch though. If you're looking for something extreme it's definitely up your alley.