Really addictive and challenging
Though this isn't the first time I've seen it, turning the tables around on tower defense is a really fun concept, and it's explored very well here. The visuals are crisp and attractive, the tutorial is great, and the branching upgrades are really fun to flesh out over the many levels. The best thing about the gameplay is that it doesn't make failure an annoyance. Replaying levels is a major aspect of the game, and whether you have success in sacking a village or not, you're always gaining infamy, and pushing your progress forward. It's a fantastic solution to the frustration of a close defeat.
All in all, great job here. I'll be playing it to completion, no doubt. Any flash game that can demand that kind of attention is a great one in my book.