That is AMAZING! It looks like OWI made the background themselves, seriously.
The only nitpick I have is that the shadow areas look a bit too dark, and you can't even see Abe in some of them I noticed, which makes it hard to know where there are unpassable walls and such.
But that might be the video doing that, you know it better since you've actually created and played the level.
Also, I meant to ask... are there any online tutorials available anywhere that teaches you to do those awesome "3D" backgrounds with platforms and shit in Photoshop?