i'm mixed about it. on one hand, the gameplay will not only be radically different control wise from the marine but also in the way the game is perceived, like having two games in one, and it will help develop different tactics for each team overtime.
on the other hand, big part of the appeal of the alien is to do get to walk on walls, do acrobatics and get in character with the creature as if it was your own skin. i think that the kills won't be as satisfying either, since you'll no longer feel like a slasher monster personally slaughtering victims. besides 3PV usually has you seeing the whole character from above, which can be troublesome in cramped spaces. and i have no idea how an over-the-shoulder perspective would work.