That's mostly what I'm worried about. I remember when Left 4 Dead came out it was awesome having the director and the four different campaigns and what have you, but after a couple months, if that, it got really boring and repetitive. I hope that doesn't happen with Brink, and I don't think it will with the Mingleplayer and the multiple different ways to approach one level; the three body types PLUS the different possibilities within those body types. I.E. you could go at a building as a light, medium OR heavy, but as a light you could probably find at least three different ways to get to the top of said building.
As apposed to L4D's linear ass, take path A, path B, or sometimes path C, but it'll always lead you to the same spot..
Edit: Oh dear god not to mention a long time after the release when even VS started svcking hard cause everyone knew all the little nooks and crannies to lie in wait in, and the survivors knew where the most likely places to be attacked at were.
I guess that really comes down to the individual. Every game is going to take the same path, just like in Left 4 Dead; you do objective A, then objective B while possibly doing side objective C, etc. Just like in Left 4 Dead, the differences come in the details. Personally, I've logged a couple hundred hours into Left 4 Dead, as I enjoy the co-operativeness of it and how there are differences, however small that difference is.
And Brink will be like "L4D's linear ass, take path A, path B, or sometimes path C, but it'll always lead you to the same spot." You have to go to the objective, and all paths will lead there. People on defense in Brink will learn where the most traveled paths are, and where the best place to put a turret is, lay down a mine, or otherwise prepare for an assault. Just like in Left 4 Dead though, its up to you to prepare and expect these often used tactics and find a way to counter it.
Edit: I concur with Wraith. You seem to get bored with video games fast, and don't really enjoy replaying any maps/levels. And if ETQW bored you pretty quickly, I don't think Brink would do anything more for you.