Its a good challenge, really makes one think about the situation, however, its not overly clear what one has to do to complete the puzzles, while there are signs showing what to do, the correct order can take a while as well as spotting how to go to each section.

The one jump to get through that gap for instance actually took me a long time to get just right to fit into that, try lowering bottom edge a bit and add in a playerclip on the top one to angle oneself in a bit easier as it got to the point I abandoned that idea and moved onto trying the next thing.

Visually a few things are off, with all the glass panels separating levels from one another it gets hard to spot where the gaps are in them, perhaps make those edges a little more obvious as well, nothing too much but a trim of some sort or mark the places needed to jump up on the bottom floor with decals pointing up.

The cube tunnel you have in the level on your immediate left upon entering the room, maybe have some actual crates and such zipping through them now and again. Add in some ambient sound for it running, while on the subject of ambient sound. Glados commentary would be a great thing to have, edging the player on, have some get triggered upon going into certain areas and such.

I must say, the gate system with the cube is a neat trick, don't think I've seen that before. So congrats on coming up with that if you did :P