Right, time for some random suggestions that haven't been mentioned yet, but go against the grain in one way or another. After this I'm off to sleep.
Cloudbuilt
I will start off by saying this game absolutely isn't for everyone. I recommend this to you if you are interested in intricate fast movement, speedrunning, and 3D platforming. Think of it as maybe a mixture of what Dustforce might be like in 3D, and a third person Mirror's Edge. That's not the best way of explaining it, but I'm struggling to come up with a better one.
Cloudbuilt is hard, very hard. When getting familiar with the game it might even feel unfair. There are some enemies that seemingly refuse to die, lasers where you least want them, and complex wall running maneuvers that require incredible precision. To enjoy the game you need to work with that, and you will need to see the enemies not as objects to kill, but as environmental hazards to avoid. Everything feeds into the one goal of the game: getting the best time as possible. Nothing else matters.
But boy, when you learn the game is it fun. I'm no Chezda, mind:
https://www.youtube.com/watch?v=26l1SndpfvE
Crimzon Clover
If you are a fan of bullet hell shooters, especially those by Cave, you should already know about and own this game. Simple as that. It is well made, with a good amount of difficulty, and incredibly fun break mechanic and scoring system.
Legend of Grimrock
You'll want to play this if you are a fan of first person dungeon crawlers. I personally wasn't much of a fan of the grid combat, but everything else was done really well.
AI War: Fleet Command
Not posting a screen of this one, because by my own admission the game looks like shit. If you want to play a very good and unique RTS though it is hard to go wrong.
Just expect difficulty, the game is hard as balls and I still don't feel like I understand it.