Hi, after having broken the puzzle month ago I've eventualy got back to solve it by more or less intended way. That time I stuck as Brainstone did. But after having figured out what to do with blue gel it was not so hard.
Actually I didn't like the way I had to treat the companion cube (being painted it bounced so randomly and often fell in the slime so I have to use quicksaves in order not to stuck in the orange gel area). Well, any other cube would do but the companion cube is like a piece of heart and even glados asked to take care of it (in Portal 1 though). Of cause it's only my point of view.
The other thing I'd like to point out is the catapult in the well - you'd better choose another animaition for it not angled but straightup.
In the rest it is very good. You payed so much attantion to detailes, animaition and destruction. I like it.
And I must admit this map gave me an idea for my last map Hard Light. Thank you.

greykarel wrote:
I didn't like the way I had to treat the companion cube

I respect...and have to face the fact that i can't fix that (without making a new map)

greykarel wrote:
The other thing I'd like to point out is the catapult in the well - you'd better choose another animaition for it not angled but straightup.

That's right ! (that was also true for the very first catapult) : fixed in the 6th version

greykarel wrote:
In the rest it is very good. You payed so much attantion to detailes, animaition and destruction. I like it.
And I must admit this map gave me an idea for my last map Hard Light. Thank you.

Thanks greykarel !