I haven't played too many truly class based games, the only ones I have experience with are Monday Night Combat and Team Fortress 2 (both xbox) but I find those games to be amazing and so I'm really looking forward to Brink. When I heard that there was only going to be 4 classes I was pretty surprised though. It seems like a low number to me. With eight people on a team and with the ease of changing classes it seems like it would have more classes to pick from.
Well, weapons are not classbound, nor are bodytypes. This way they removed the need for a "tanky" class or a "damage dealing" class.
That being said, I only regret that there's no more Field Ops like in their previous games.
Choosing a class only affects which objectives you can do, not your strenght or weaknesses in a battle.