^^ Yeah, the amnesia bit is too hokey.
They'll start season 4 several months later (as they did with previous seasons) and Beckett will be recovered, physically at least. She heard what Castle said to her before she passed out, but she's going through so much sh*t that she can't deal with it right now. Castle will be there to support her, and not push the relationship thing until she's ready. Beckett will start seeing a therapist, and will want to move slow with Castle.
Montgomery was pulling police files out of a safe at his house, and he sent a letter somewhere, so I'm sure those will play a big part in continuing that storyline.
I'd like to see Esposito and Ryan get more to do, maybe have Castle work just with them for an episode or two as Beckett is recovering.
Damn this show. I love it too much!