Nobody knows how the BRINK gameplay will feel. Actually, the testers will, but as for 'feel' I think it's something that cannot be described unless you have a really quality player explaining the game. Since I've never heard of a skilled FPS player being hired to test an FPS game and report on it, I imagine we'll just have to wait and see.
I've burnt out on BC2 about a month back, been playing Monday Night Combat and Breach since. These games stretch a very wide FPS gameplay gap. I'm sure as soon as BRINK comes out I will have an arm and a leg up on just about most people. But that will mostly just be from playing FPS games for a over a decade.
Well myself, and others on this forum, not only have decades of FPS experience, but also extensive exposure to SD's previous games, which follow the same fundamental gameplay formula as Brink. Where you may understand the the basics, such as aiming and shooting, we will enter the game already knowing pretty much how an entire match is going to play out. We will know what class does what objective, how missions work, how to already play classes effectively, we will already be used to the "too many bullets to kill" mechanic, what most of the HUD elements are, etc.
So whatever "leg up" you may have on the competition, chances are, veterans of SD games will have 2 legs up on you - wrapped around your neck, putting you in a headlock.