Cool 3D Desktop with CompizThose looking for a quick solution can use http://live.linux-gamers.net that allows you to create and start gaming from the live CD/USB directly.
In addition to the point and click games(like card based games), you can have some serious fun with 3D games that PC gamers have become familiar with. Be it a fast paced action game like AssaultCube or a racing game like TuxKart, there are options for everyone.
TuxKart : Funny racing game
AssaultCube : Fast paced action, a la Quake3 style
Thanks to ID software's initiative of providing a linux binary(and their stand on DirectX framework), we can install and play a game like DOOM3 on Linux http://sites.google.com/site/lgmscripts/scripts/games/doom-3 (which is definitively on my TODO list:)
There are certain caveats to this excercise too. Since my laptop has a Nvidia GeForce 8200MG card, I had to use a non open source binary driver as the cannonical one was not working well on Ubuntu. If you consider the freedom and the non presence of any cost/license, it forms a good overall personal entertainment package.