If you have a few hours to while away on a browser-based flash game, give Bloons Tower Defense a try.
This simple-strategy game requires you to pop a stream of bubbles, not allowing any of them to escape out the other end of the track. As you move though Bloons Tower Defense's levels, you'll be given access to towers that will allow you to shoot down the balloons in new and imaginative ways.
Every balloon that you shoot down in Bloons Tower Defense is worth money, but using your towers will cost, so it's up to you to distribute them as efficiently as possible. Letting balloons escape will cost you lives, but if you get desperate, you can get a once-off injection of both money and lives.
You can play Bloons Tower Defense without registering, but to access the save facility and other, social network-like features such as a profile and message service, you'll need a free account. You can also upgrade, which will give you access to new tracks and upgrades, although you already have a decent selection in the free version of Bloons Tower Defense too.
Bloons Tower Defense is a simple game that will keep flash fans entertained for a few hours. The rest of us will be seriously underwhelmed, though.