Portal 2 wasn't nearly as messed-up as it could have been. I loved it, and still pop in now and again to enjoy the physics and writing, but I always wish they'd went further and curly-wurlied the gravity and surroundings. Every time a room was fixed in front of me, I wished the same tech was used to just turn everything upside down, inside out, or that it would twist the testing chambers into odd, broken configurations. I am a very needy person. With that in mind, I'm interested in this Greenlight begging puzzle game, Tri. A FPS puzzle game where you drag out triangular walkways to cross the world.
As far as I can tell from the trailers, those walkways will be able to take you from the ground to the ceiling, so you could end up upside-down attempting to solve the puzzle. You can't just make the triangles in thin air though, but instead you need to be able to connect three things (floors, walls, ceilings or other triangles). You also can't intersect other objects with your platform. Those are the rules that govern the journey through towers, dungeons and "vertiginous abysses".
It's already out, and costs eight bucks/ten eurobucks. It's made me want to hunt through Portal 2's Steam Workshop to see if anyone has turned out a really freaky. I don't even need puzzles, just interesting, messy spaces messy spaces.