Bug Battle Combat by FineFin Games fulfills my two criteria for a fun Flash game: 1) it's easy to play 2) it's mindless fun!
In this game you're a square swat paddle that squishes bugs on contact. You've got to protect your base from the swarm. If you think it's easy, just wait till there's a LOT of bugs comin' at you.
Link (on Neatorama) - via ArcadeTown