Action games
If you don't play games that much, there is a big chance you have played an action game, e.g. a shooter, at some point. This category is full of games that won't let you get bored.
Killing Floor
Danger Zone
Rise of the Machines
BZFlag
Alien Riposte
After The End
StickMen War
AirStrike 3D: Operation W.A.T.
Shamanville Earth Heart
Dark Age of Camelot
Red Faction II
DROD: The City Beneath
Half-Life 2: Episode One
Half-Life 2: Episode Two
Engine of War
SpaceForce - Rogue Universe
Memory Wiz
Shade - Wrath of Angels
Swarm
County Fair
Bad Toys 3D
PayDay 2
Mighty Rodent
Dragon Fist Legend
Larva Mortus
Bomb John
Sailor Moon
Discover FDM
Add-on support
You can get add-ons that download files/video from arbitrary websites.