I really like the brushwork, especially on the floor. It is different then just a plain floor and gives it a cool floating look when you can see through the glass.
The lighting and texturing is good, nothing out of the ordinary but it works with the map.
The layout is the only thing that should be improved upon. It's a simple layout that has been remade way too many times. try some different designs to improve the gameplay and fun value, instead of just the four blocks.