The prequel to the Half-Life mod called Rebellion.
The mod is good, with decent length. and it has awesome cinematics, the level design is not bad at all with beautiful open areas and deep water. also this mod doesn't hold your hand and you can explore alot, I am not even sure if I explored everything...
the ending cinematic is bloody epic too but the detail of levels seems to fall short in the end.
You should totally play this if your bored with nothing to do.