- The spheres reflect a sky. I'm pretty sure you could have fixed this with a cubemap.
- Some problems rendering portal effects on surfaces that are not able to have portals, but I bet this is due to the next point.

+ The rotating room. Brilliant. I don't know why valve chose not to include this element into the game, because in my opinion it works very well.
+ Use of sounds. Hearing the AI chime in with completely relevant comments while I was playing made me feel like I was back in an Aperature test chamber I had missed while playing through Portal.
+ The sphere. Again, another new element that feels very much like a part of the Portal universe. The mild bounce and roll its shape presents to the puzzle makes it very unique from the cube I expected to pop out of the delivery tube as far as how the player can use it in the puzzle.
+ Difficult. I admit it, I can't get the energy ball done. I know how to, I think, so if I gave it a few more tries I bet I could do it. Yeah, yeah I know, reviewing the map before actually beating it but I've done everything else and couldn't wait.

- Difficult. This is a negative as well, just because some less experienced players may find it frustrating. It is very complex, specifically the aforementioned energy ball part. Damn that energy ball. However, even though I failed repeatedly at racing to get the ball where it needed to go, I still want to go back and try again. If the map weren't so damn fun, I wouldn't want to bother.

Summery: If you love playing Portal for the sake of solving new and challenging puzzles, you'll love this chamber. Very well done, but then again I expected so from a professional designer as yourself. If I were vALVE I would be giving your ass a job offer to make bonus map packs instead of writing this.