My current thoughts on it is that it's a really amazing tool, but it doesn't quite have everything that it really should. I really hope (and assume) that Valve will update it with more items, diagonal surfaces, doors, lights, and so on. I haven't tried decompiling a map that I've made in the editor in Hammer yet, but I'll probably get around to it eventually.
So what are you guys' opinions on the map editor so far? Too simple? Too complex?