I just played your map, and for a first map it's quite good. I particularly liked the rocket/doors puzzle.
However, I have a nice long list of bugs that I think you need to squish before considering this map for release.
The main thing I noticed on my first playthrough is the extreme amount of misaligned textures. This is the case in virtually every room. In the corners, the textures end half way across, which detracts from realism considerably, and many walls have obvious seams on them where textures haven't been matched.
The first room in which you wake makes no sense to me. It has a "behind the scenes" feel, which wouldn't be so bad in itself, but GLaDOS talks to you when you leave the room as if you are just a normal test subject. If I were you, I would make it so GLaDos is somewhat surprised by your appearance there, if you choose to stick to the BTS theme.
You should also work on some kind of voice for this first room, as the text doesn't fit if you are using voices for the rest of the map.
After you leave this first chamber, GLaDOS refers to the Companion Cube as the "Weighted Storage Cube"
The Companion Cube only seems needed for the first button, if I use what seems to be the intended solution to the map. There is no need to take it with you at all, which to me takes away the need for it to be anything other than a normal storage cube.
However, you do not even need to use it on the first button, as the entire level can be completed without touching it. There is a small gap in the green area above where the cube is, which you can shoot a portal through. This bypasses the first button, and takes you behind the turret in the next main room.


If you like, you can also take the cube with you to use, instead of the turret, but like I said, you do not actually need to touch the cube to finish the level.
The room right at the end has a few problems as well. Firstly, one half of the door appears to stick out of the wall when you open it.

And, when you get to the Cake, if you turn around, you can see some of the level through the skybox.

Other small issues:
This may just be down to taste, but the glass texture you used seems really ugly to me, and doesn't fit with the Aperture feel. You should also think about adding window frames, for appearance's sake.
You need to add some sounds to the buttons when depressed, as I didn't feel I was getting any feedback from them, like you would in the normal game.
You should read up on "func_portal_bumper" and their proper placement in this thread.
Don't let these issues put you off though. The map shows genuine promise in some areas, and I enjoyed playing it, which is what matters most. I tried to point out the negatives more in my post to help you improve the map, which I guess is the point of beta testing.
Good luck with this.