http://www.naturalselection2.com/download
If you preordered the game you can download the alpha version of the level editor.
They have two tuts: http://www.naturalselection2.com/tutorials
From what I'm seeing, the interface is really nice and clean with minimum clutter, which is how I like it. (looks at UnrealEd) Making stuff is fairly intuitive and reminds me of SketchUp.
Anyways, give it a go. I might preorder the game, it's not that much of a fortune (and congrats to the devs for not setting up a ridiculously high price).
EDIT: looks like the price was bumped up from when I last checked. A few months ago it was 15.99 I think, right now it's 19.99
I am not sure whether you need the special edition to get this, though.-











