One of my favourites so far - though I'm not sure if I actually completed the puzzle the way it was intendeed, or if i just cheesed my way through it.
For those that are interested, after getting the blue switch on I pushed one of the 4 carts arranged in a square to the left of the switch room back with me and the key to the start and down, so i could push the key further through. If this game was meant to be open ended, this is great, if not the game is still really good. gets a 4/5/5 from me.