Facebook app War Commander, a strategy game reminiscent of Red Alert, is actually pretty fun.
The game lets you train units, gradually build up a base that includes defensive weapons and resource-gathering buildings, and fight off enemy attacks.
A quick tutorial shows you how to command your units to move and attack, as well as how to build structures.
The game also provides the inevitable instructions on how to share your feats with your Facebook friends.
The downside is that, like most Facebook games, War Commander requires you to wait around for your resources to increase until you can buy something else.
The idea is that you will be doing other things, and come back to Facebook and continue to play.
This stops you from playing a large chunk of the game in one sitting, but it is fun while you're playing!