They're surprisingly fun and I wonder why more team deathmatch games don't include them.
I used to play Tremulous and it was super addictive to live and die by your base elements. Gives the game a whole new dimension about strategy and teamwork.
Apparently both Natural Selection and Tremulous were inspired by the Gloom mod for Quake 2, according to the Tremulous FAQ:
Development on Tremulous began long before NS was in the public domain. If Tremulous is inspired by anything, it is inspired by Gloom for Quake 2. NS has a similar ancestry (please see Game Developer Magazine February 2001 issue); this is probably where the confusion arises.