Addictive.
This definitely ranks up there with the top defense games. There are some nice upgrades and the addition of a player controlled shield makes the game a little more challenging. The first few levels, as the authors have said, are easy but it allows you to get your bearings if you need to.
I can't remember playing an enjoyable defense style game that didn't have a medieval/fantasy theme until now. The graphics, style and sound reminds me of Worms, maybe it's because of the wind and weather element- nice touch by the way.
A lot of time and effort has gone into this game, right down to the cool custom preloader, and the skill of the makers is undisputed.