Mirror's Edge mostly pursues a realistic style, with a very arty colour-design.
BRINK on the other hand has that "hyper-realistic" style and a very dirty colour-design.
I don't find them to be very similar.
Well...
MORE like Mirror's Edge than FPS games, anyway.
It's got exaggerated body and facial features for the characters, unlike Mirror's Edge, but both games have a lot of contrasting colours, and more vibrant colours rather than the dull greys and browns most games with first-person perspective stick to. The "proper" buildings are bright, and use white and pale grey a lot - stark and almost "clinical" in appearance in both games, but the world also has colours, and those colours are vivid, standing out against the harshness of the well-built structures, and against one another. Also, compare a wide view of the Ark to any angles you can get on the Shard in Mirror's Edge - I'd call the architectural styles of the games similar. But Mirror's Edge is at the beginning of the fall, where things can turn around easily. Brink is set well past collapse, and into the time where people are trying to rise from the ashes they've buried themselves in.