I disagree with most here as I don't believe playing as the Alien will diminish it in any way, we have all played as the Alien before in other games, it never hurt the game then and won't now. Oh and the "have to remove invincibility" thing is not a bad thing because the Alien is not invincible, not in-universe anyway, it was a game mechanic to ensure you couldn't deal with the threat....otherwise the game would be very short wouldn't it?
But I can understand everyone concerns, don't want to take steps back now do we
but CA made a good game, I believe they can easily make a good Alien campaign without screwing things up like others did, also it would be refreshing, all that pent up frustration at pesky Joes and humans, now you get to hunt them. As for the concerns about not portraying the Alien properly, sure you can. If the Alien has to get hosts for the hive, then one of your goals would be to have sneak and take one human at a time without killing him or her and without getting spotted and so on, there is so many ways for the Alien to be played instead of the usual wanton slaughter.
I would like an origin story about the main Drone, how it came to be, how it helped start the hive for the Queen, plus we really haven't played as a decent Alien since Alien versus Predator 2. I speak for my own view here of course but I really can't stand playing as an Alien in AVP2010 and A:CM, just too low down, I wanted to play as the terrifying 8ft + warriors but you pretty much run around like a dog Alien and get gun-butted to the floor by marines. At least in Aliens versus Predator 2 gave you the choice of Alien type and the crouch button, which allowed play styles.