I've used it and I'm still exploring it. The source was just released recently, and there's a Github community, forums, and subreddit for it. I like its scripting language. Dynamically typed, procedural or object oriented depending on how you use it, and there's support to edit class attributes created in script from within the Godot editor without touching the script (good for community projects, distributed classes, etc).
There's not a whole lot I can say about it yet since I haven't gone past 2D. I'm taking my time with it, letting them complete features and working my way up to the good stuff so that I have a decent script library. The fanciest thing I've done so far is point in polygon detection since their polygon interface is a little obtuse and it was just easier at that time to write my own than to reverse engineer theirs.
It's not from MIT. The developers are OKAM Studios, and I think they're in Spain. They're working on something for Square Enix lately, so while Godot has daily builds, some things (like documentation) are coming along very slowly. Since it's open source, in time it should become a viable alternative to Unity for those who don't want to buy a license, and the license is completely open. Make whatever. Sell it. Don't. They don't care about that; they just want to share their work (pretty awesome of them).