Onslaught - Today's Time Waster
If you got addicted to Desktop Tower Defense, you'd probably better not read the rest of this post. Onslaught is another in a long line of tower defense games, but a darn good one. Where Desktop Tower Defense feels a bit constrained, Onslaught has a bit of a more organic feel to it. The concept is the same - there are attacking "critters" that are trying to get past your defenses. Your job is to build defensive towers with varying abilities to stop the critters from advancing.
The graphics won't stun you, and many of the critters are hokey icons, for example the printer icon in the screenshot here. But if you can overlook that, the gameplay is strangely compelling. There are lots of ways to combine weapons and make something much more powerful, and the control mechanism is very easy to pick up.
Heed this warning: if you value your time, don't click through. If you do, you'll probably lose an hour or more before you know it.
