Ok I understand CoD is a great game, I'm not saying that its bad, I'm just saying ET is still a great game.
In ET you can do many "tricks" to outwit your enemy. For example in the map Oasis there is a wall to destroy, instead of destroying you can use a technique called "strafe jumping" and trickjump over the wall. That is just one example, trickjumping adds to the game element, clans have to use it and counter it in ladders. (Other tricks might involve making human ladders and "wall hopping")
Almost every week a new map is released in ET. There are so many creative mappers and they make maps which you can do so much.
Escorting Tanks, Destroying Walls and buildings, Stealing golds and documents, and mix of things.
With server settings with the ETpro mod, there are many crazy things you can do. Also there is a promising mod that is in the making called Price of Peace.
Just saying ET is continuing to expand and there is just much more than killing your opponent. (Sorry for the long post)