By the way, to answer the person who asked about other games using the single-player-progression-in-multiplayer-game concept, Enemy Territory: RTCW did that in some, perhaps even most, maps. Some maps were more like TF2 "push" style in that you could capture a spawn point and start spawning ahead, but if the enemy captured it then you would end up behind again. Touching the flag for an instant captured it...I don't remember if some spawn points required remaining in the area like in TF2.
Other maps had progressions, where you had to dynamite a wall or something, and if you could manage to protect your engineer, get the dynamite planted, and not have it disarmed in a certain amount of time, you would spawn forwards for the rest of the map, spawn times might be changed, etc. Fueldump was like payload -- you had to escort a tank, blowing up walls as you went along, and the tank only moved if you were next to it I think. In the end, the tank blows open a fort so you can dynamite a fuel dump...assuming you weren't playing one of the map versions, such as vanilla maybe, that allowed you to use a covert ops to sneak an engineer into the fuel dump and blow it up ahead of time.
There were a lot of good things about that game, especially for a totally free FPS with lots of mods and custom maps, though I mostly liked playing on EXP-save servers so I could have all the top-level abilities and such. It's kind of surprising if TF2 people haven't ever tried it.