I really liked it, so much so in fact that I didn't want to finish the demo as I want to experience the rest of it in the full game when I eventually get it.
Visuals were decent, gameplay was quite good although I'd echo some of the complaints about overuse of the 'mimic' mechanic by enemies. I like the Portal meets Bioshock meets Alien: Isolation feel, it seems like some of the areas will be quite big and be fun to explore. As someone else said already, input lag and LOUD MUSIC is going to be addressed for the full game.
I was quite impressed with one of the early sections where you can change the helipad scene to the two different rooftops. I did that, then turned the skybox on, then smashed through the roof of the apartment and thought I'd got myself stuck in that area because I could no longer find the exit, but was able to smash the 'screens' and get back out. The level design is very well thought out.