I will post a much improved version soon, I won't bother with this.

As always, first releases need a bit of work. However, yours doesn't need much. I just think that if it weren't for the fact that goo doesn't kill you instantly in this version, I'm pretty sure the last chamber can't be done. At least, I couldn't find a way to do it.

My reccomendation would be to add some way of accelerating yourself out of the angled platform, then add a grate on the other side of the hole in the wall, where you would presumably land.

Looking forward to future releases

i must be missing something really obvious but i get into the door and use the cube to get to the first platform and then i have no where to go...

I guarantee you it is possible and no glitching is involved. You have to look around and find all your resources. I don't want to give too much away just yet. I'll add a couple hints scratched in blood.
Meanwhile, can you tell me if there are missing textures via noclip?

Done it. I don't know if that was the solution but about the 45? jump, I had to jump on the Companion Cube and then jump on the black frame of the door and place a blue portal in the ground to do it.

That isn't the simplest answer, the intended solution doesn't require flinging. Good find though.

Can someone put this in [WIP] section?