I found this the other day. It looks like a simple tower defense game, and it's a Flash game so it doesn't seem like it would be much.

Then I played it for SIX HOURS. For a free Flash game this is amazingly good, and if you support the developers you get to unlock premium content which makes the game even harder.

It's just a really good, interesting game that's completely free.

http://armorgames.com/play/12141/kingdom-rush

Check it out and enjoy!

______________________