Simply put TF2 is Wolf-ET without the objectives besides capture the flag and control points. It was intense because it was close quarters, sorta like twitch gaming.
Quake Wars from my 2 experiences was just very sparse. Even on full servers everybody seemed very far away.
I've always believed when you add vehicles to a FPS it essentially is no longer an FPS, because you are always going to prefer driving and using the heavier guns or faster vehicles to walking and gunning. They should call it V-FPS.
I've played UT2K4 and it was just not as fun as the original UT.
Advice to FPS makers of the future: keep the vehicles out otherwise make it so you don't need to get out.