I'm day one for this, Valve wouldn't make this unless they knew it was going to be amazing.
I believe this is well. Valve is so ridiculous with their quality control and taking time to do anything - if they release something you know it has some genius brainpower and thought behind it so there is no way they would release something sub par. They are not known for rushing so there is no way that when this comes out it is going to be anything less than excellent.
The fact that they are giving this to developers now shows that they are committed to releasing something great.