I like this, though also found the first level a little hard to begin with. It may be simpler than the others, but in some ways I feel as though that gives the computer player an advantage: the multi-flag levels seem easier because you can end your turn leaving no safe sand to take (and they're more forgiving because if you screw up once it's not an instant lose).
What do the rocks do, by the way? Were they intended to knock over flags they roll into or are they just a fun little extra? Either way the physics are very satisfying - it would be great to see more games like this.