The Companion Cube took me 10 minutes to find, and it was the last cube I had to look for. Maybe I'm just dense, but it was really frustrating.

I really like this level. It's probably the perfect length for a level too. But I do think the rooms are slightly larger then need be and it just makes walking around a bit tedious.
Laser room is easy to beat by using portals on the ceiling and dropping down where all the cubes are located. Not sure if it was intended to be this way, but it makes that room maybe a bit short. It's easy to miss because it's so dark up there, but in the elevated section with the button, the ceiling is portal-able on a few tiles too I noticed. It might be nice to add a light inside there also.
As for the other room I enjoyed that one quite a bit, short and sweet. I love the sort of hidden cube, it took me a second to find and I enjoyed searching for it, very easy to miss it.
I think it would be nice if there was a way to portal from the first room into the others for quicker movement around the map, but besides that I really enjoy this. Hope to see some other stuff from you :)