This the last, and best, Flash game I ever made. It's very simple but it's fun and challenging and certainly worth a play if you're looking to kill some time. If you get stuck, enter the password "custom" and you can make levels with your own mix of enemy types.
I got my start programming with flash games. Actionscript and Flash presented an easy-to-grasp object oriented model. I was sad to see the technology get so thoroughly disrupted, but I was lucky to be in an environment where I could learn about the new JS and CSS driven interactivity paradigm.