Guessed by @Mnementh
A one-of-a-kind experience. There's no game out there like Thumper, and there will likely never be one. This fact just makes it that much more remarkable that the game is so incredible - there's no real guideline to work with here, it's a completely unique concept. To get it this right is just unbelievable. At what it's trying to do, I can't find any flaws with it, not one. It's perfect.
What I really like about Thumper is that, despite being a rhythm game at its core, it still uses a lot of good ideas in level design. Rhythm games are generally designed around the music, and while there is an element of level design involved in creating a track that feels good to play with the music, the approach here is the complete opposite - it feels like the music is designed around the level design. All the levels you play through in the game tend to have a clear progression and structure, introducing simple beats at a slower pace that get progressively more complex the further you go; it starts off pretty simple just ensuring you get the basics right, but then slowly teaches you about more tricky moves you can (and sometimes have to) make, which earn you more points and style. All of this is done in an entirely organic way, and every mechanic is introduced in a way where you can't get past it without learning how to and when to use it. When you begin to master all the tools at your disposal, and manage to get a good string of nice moves going, it feels absolutely incredible - which is just unbelievable when you consider that the game uses nothing more than one button and the directional input. It does so much with so little.
(Speaking of doing so much with so little, did I mention it's less than 1GB and runs like a dream on all platforms? Yeah, there's that too.)
Then, there's the atmosphere... man, the atmosphere. The stunning art direction and sound design combine to create such an oppressive atmosphere, it's very hard not to be completely immersed by the experience even when playing it on a tiny handheld screen (never mind on VR, that's totally mindblowing). It's promoted as a "rhythm violence" game, and man, it really does succeed at giving you that feeling of visceral violence, of pure hatred for each boss that shows up on screen. In fact, for as weird of a concept as bosses are in rhythm games, this really succeeded in making them extremely memorable, due to a combination of the atmosphere and unique gameplay surrounding each one. And everything this game achieves, it does so without any kind of a story. Yeah, you're a beetle flying through this weird dimension fighting off cosmic creatures by hitting the floor. Is there anything we need to explain? No! Just take it for what it is. This is a quality usually reserved for less serious, childlike settings, but this game proves that even outlandish concepts like this can be taken seriously without any exposition.
I really do only have praise for this game. Ever since introducing it on my list back in 2017, it's only ever gone up year after year. I don't know if it'll continue it next year - moving up for 4 years straight is unprecedented, never mind when it's already this high -, but as time goes on, I find it harder and harder to find anything negative to say about this game. Every time I feel like it's becoming a thing of the past, I end up booting the game on a random day and am completely soaked up by it all over again. There's no escaping it. Even just talking about it has made me want to go back and play more. Thumper is a masterpiece in rhythm games, it's the best thing that's been made in the genre.