Amazing graphics for a web game. This is an ambitious project in two ways: destructible environments AND vehicle building. For the destructive environment - it worked OK, it doesn't look to be physics based, is it? Have you considered using voxels? I've seen a few commercial projects which use them precisely because they are suitable for destruction.
One suggestion from me is to spawn the character right in front of the button and place a diagetic indicator (in the game world itself) or at least an indicator at the center of the screen. It's easy to miss the menu on the side and it has a lot of text - the button is not highlighted.
Good luck with this! It will be interesting to see where it goes.