It's looking great!  A few comments:

- For the night islands (e.g. The BitLands, the third of the demo islands), we have beautiful starry skies and the dramatic eclipses together.  It would be even better if the black disk, that is obscuring the bright moon, also blocked out the stars.  It would give us a real impression of a dark moon passing in front of a bright one.

- Alternatively, the moon at night could have a phase, rather than being eclipsed.

- I think the islands with realistic colours look much better than those with bright, alien colours.  Maybe realistic islands should be a lot more common than exotic ones?  I suspect that part of the problem is that, without raytracing or similar advanced techniques, the brightest coloured objects don't reflect any diffuse coloured light to their surroundings.  That's OK as a style in a realistic-looking island, but with the extreme colours it all looks a bit too artificial.

- Movement was a bit odd.  I appreciate the really high jump, but sometimes I was walking very slowly even with sprint pressed.  Are some terrains (e.g. long grass) supposed to slow us down?

I haven't found any "rare" things yet - I'll explore more thoroughly when it is fully released.  But I'm looking forward to it!