I'm downloading it right now so I can't tell you how far along it is, but remember, it's still a beta, and it's quite the monumental task to convert Doom 3 into a Thief game, which is why it's taken this long to get to this stage even. It's been in development for quite a long time, but at least by now you know the guys involved won't simply just quit at the first sign of trouble.
For those who want eye candy, here's a random youtube video. I don't know what settings it was run under, if the player knew what he was doing, or if it's even a decent mission shown as I haven't actually watched it so it doesn't necessarily represent the actual content. Explore the website I linked above to see examples of the very high quality content that is available for mission creators and, if this video fails to impress, at least you can rejoice at what the future holds for the Thief communities, as, again, that's their primary target.