Hanzawa Naoki came back for a second season if you are a fan of that show. I would also second Unnatural. I love that drama! In terms of romance dramas, Koi wa Tsuzuku yo doko made no was pretty popular.
For Korean dramas, the following were really popular/talked about a lot:
Because this is my first life (didn't watch this but heard of the good reviews)
Goblin (it's a Kim Eun Sook drama....had lots of fans and was talked about a lot)
Prison Playbook (would personally recommend)
Weightlifting fairy kim bok joo (most people who have watched it loved it...it's a school romance)
My Mister (also would personally recommend)
Sky Castle (very talked about drama.... personally, I thought it fizzled at the end)
A-teen (an unexpected hit I believe)
Hotel del luna (a Hong Sisters drama)
Crash landing on you (drama from the writer of you who came from the stars...was very popular)
Stove league (didn't watch but heard lots of good reviews)
Kingdom (this is very popular and fits the horror genre)
The world of the married (also widely talked about)
