Because i was so freaking bored i downloaded it and played it.
Looks and plays like the full version, no surprise there.
I'd forgotten how damn cool it looks when the imp(?) shows his ugly face for the first time. Looks fantastic when he crawls over that pipe.
I cannot wait for a "real" game to use the D3 engine. Not that D3 is a bad game, i enjoyed it a lot, but it feels a bit like a tech demo.