Alrighty I'm impressed! The demo seemed to run just fine on my laptop.
A couple of things would be nice;
1) ingame options such as inverting the mouse look!
2) ingame listing of the keys, perhaps with the options or on pause menu - this is especially important since it automatically goes fullscreen!
3) a choice to run fullscreen / windowed.
4) I seemed to be able to look further than straight up which was very confusing.
And a possible bug, I headed straight for the water line when the game first loaded and found that I got totally stuck in the water for a while until I dug myself out by creating a trench into the land. Possibly a bit disconcerting for first time players.
Otherwise I really like the look of the whole thing, you've really got a beautiful game there. I especially love the combination and balance you've achieved with the water, heavy fogging/atmosphere and bright colours for the landscape. I'm a huge sucker for blue skies instead of all the usual drab and dreary crap we get in most games and yours is very pretty.
I might try and hook my laptop upto the downstairs TV to get an even bigger screen to play it on!