Yeah, the constant change in your team line-up is a bit annoying, but as a device to drive the story it does its job.
What annoyed me the most in the beginning were the characters, which meant that the first few hours of the game were like pulling teeth to me. Soulless female soldier, stereotypical black dude, cocky slab with can-do attitude, shrill and bubbly teenage girl, mopy speech-impaired coward - all of these guys get better later on, but in the beginning they're all one-dimensional and stuck in personalities and behavioral patterns virtually designed to make the player scream in exasperation. Fang is the only character I really liked from the moment she made her first appearance, despite her weird accent (what is that, Australian?).