There is no demo, I'm affraid. The only demo there is is a tech demo, which was released AGES ago, and as such has been improved greatly since, with new features, faster rendering and gameplay, aling with many other improvements. All the demo featured was a room we could walk around, and toggle things such as water and refration to show what they look like. It had no editor or gameplay (noguns, pickups or enemies) at all.
You'd be best asking the Beta testers for oppinions.
~Flash
Hippopottomonstrosesquippedaliophobia