Sorry for the long delay in responding, everyone - been away from home for just over a week. I've just updated the map to fix the bugs that wildgoosespeeder mentioned - many thanks for pointing them out. I don't think it's very easy to do the second chamber out of order now, though I suspect one of the resident ninja will prove me wrong on that point....
@Kenn Kong - yeah, you got most of the solutions as intended, aside from the way you got into the green room (which won't be possible any longer) and taking a long route back from the top room (You should be able to shoot the bridge out from where the camera is and easily make the jump down to the railing on the left).
The way you got the cube back at the end is the original intended solution, although there a couple of others that I purposefully left in that are arguably easier. I really like how you made it to the exit at the end - not exactly what I had in mind, but cool enough for me to leave it alone.
I might post an intended solution vid sometime later on anyway. I think my best time is about 5 and a half minutes...
By the way, do you play with a controller?
Also @PCDoc and Haggis - Thanks for the praise! always good to know people are enjoying it.