Top 5 would be:
Jinrui wa Suitai Shimashita (Humanity Has Declined), I had no idea on what to expect on it besides that some of my friends liked, and it turned out to be one of my favorites of the season with it's unique setting, cynical main character, and often dark satirical humor, not what I expected from the colorful art of the show
.
Natsuiro Kiseki, I had expected a typical SoL cute girls doing cute things show, and instead got something more interesting with actual character development with some drama, while still keeping the humor generally, it was much more enjoyable than I expected.
AKB0048, I have to agree with early posters the premise did seem silly, but somehow the show really make it work.
Accel World, honestly I had written it off from ep 1 due to the MC design and personality initially, though after my anime club picked it up, and I watched more of it and found it got better as it went on, and it had a great sound track.
Girls und Panzer, I thought this would end of with K-On level focus on the tanks, but in actuality it's put plenty of focus between the girls and the tanks, and actually had good battles for the show thus far.
Others:
Sakurasou no Pet na Kanojo
Hyouka
Chihayafuru
Haiyore! Nyaruko-san