So. Brink, besides being what a racist caricature of an Oriental person would say is their favorite Doctor Who episode, is also a disappointing game. My feeling is that it needed to stick to its guns, or rather, pick a gun to stick to and then stick to it. Are you going to have a story or concentrate more on your round-based competitive multiplayer? I don't think you can make them work together, they're like the straight-laced young new detective teamed up with the cynical old-timer except without the opportunity for a buddy movie. If story matters to anyone it matters to single players, the co-ops are busy chatting amongst themselves and the competitives would rather focus on having the most headshots.
For me, Brink's biggest mistake is forcing the player to unlock everything. I don't have a marketing degree but I would have thought you want your game to put its best foot forward and leave a good first impression, not dangle its content over our heads and say "Oh, you want this? Well, then dance for me. Sexily." I'd have thought that if you want to rely on using customizable outfits to let players make their avatars distinct from each other then you should have started off with more than two outfits available from the start. Perhaps the engineers should have started out with the ability to build sentries or the soldiers should have started out with miniguns, or was this all part of the devious scheme to avoid getting compared to Team Fortress 2 some more (take a shot)?
Still, if you're resigned to getting compared to Team Fortress 2, I think you should go in the other direction. Don't have less character classes than TF2, TF2's already pretty streamlined (or at least it was before they started bringing out new weapons every other weekend apparently in paralyzed terror of people getting bored of it, and incidentally that's three shots this paragraph so far). What you need to do is have more classes. Make it the MUGEN of class-based shooters. After all, there are many facets of warfare that the TF2 lineup doesn't cover (four shots).
Here are a few possibilities I've come up with:
The Propaganda Artist
A good starting point for design is to take something that already exists in a game and find a new use for it. Custom graffiti tags have existed in Valve multiplayer shooters since the first Half-Life, but only the Propaganda Artist will employ them in gameplay. The Artist's job is to take a candid photograph of a member of the enemy team who's being a particular pain in the arse and get it back to base so he can create unflattering cartoons and then paste them all over the battlefield. The Artist's teammates gain a morale boost as they realize that yes, he really is just a silly old bugger with a fat neck, and thusly shamed the victim will have no option but to slink back inside their base and cry, I would imagine. The Propaganda Artist's other main duty is to remind his teammates not to sleep with the local women.