You're right, the twist was probably obvious, although they seemed to be trying to lead us to think that it was Sawyer and Kate's baby - and that she lied to him. Its an interesting twist to be sure, and leads to the question(s) of why Jack doesn't want to see Aaron (something with Claire most likely - and if he found out they were related at some point). Also, what happened to Claire? I'm really having fun watching this season - we're actually getting some answers, but more questions as well, and it sure has been interesting.