Definitely a new spin on the defense game. Very interesting use of traps and settings to really push the boundaries of the genre. Interface was well designed and easy to use and the learning curve was easy. A very good implementation of strategy as well - you can't just lay random stuff everywhere and hope to survive long (which happened to me the first time around)
I do have some qualms, however. I think you need to allow more time to edit and create your traps between waves. I found myself rushing to set things up in time and some times before I got done the nasty little pirates had escaped through the gaps in my system. A little bit more time would've helped greatly.
And a little more variety would be great too. I know that's asking a bit much from an already original system, but I found myself looking for more alternatives to kill my pirates aside from pushing them into stuff. And might I suggest upgrades for the swingers as well? I mean, their primary purpose is to push guys into the traps but you also made them deal damage. You could expand on that and try and give that thing upgrades too.
I think the map layout was a bit pointless as well. I'm not sure about the other guys, but in order to really make the traps effective I ended up blocking two of the three bridges just so that I could get the pirates where I wanted them. This in turn made the lower space of the map completely useless. I don't know if that's what you intended to do, but useless space is useless space. Maybe put the bridges lower down the map or eliminate the lower space altogether.
You might want to add the option of destroying the stones on the floor for a price. Of course this might be intended as well to make it just that little bit harder, but I was a little frustrated that my master design was going to be blocked by some unmovable stones.
This is a really great concept for a defense game. And a great silly song to accompany it. A good refreshing take on an old classic genre.