Everyone knows that you can’t make a particularly new game without using things or ideas from previously made ones and Counter-Strike: Source is no different as it has the same blood the grandpa Quake has.
As you can see in the picture below, not only Quake 3 and Doom3 are coming from the
"House of Quake" family (link via Kotaku), but also some infamous names as Half-Life 2, StarWars Jedi Academy or even James Bond 007 Nightfire.
Whether some of these games are considered to be a rip-off, a successor or just a look alike, they will always have something from Quake and the list will keep growing as the other games will have their new generations rise.

thanks for showing us one of the oldest generation tree of the internet...
I think there are like no really good shooters beeing not either made with a quake or unreal engine?
and probably many others that i can't think of right now.