I'll join the crowd recommending Signal (2016) and Healer (2014) as a must-watch. These two are my favourite dramas of the last years hands down.
I also enjoyed Angry Mom (2015) and Twenty Again (2015) where mature women are suddenly thrust into a high-school or unversity environment - the ensuing hijinks are hilarious, although the dramas deal with many weighty issues as well. It's a nice balance and I really liked them as a change from sageuk or fusion dramas.
For ghostly themes Oh My Ghost (2015) was good as well with the cast delivering many wonderful moments.
I'll probably watch some of the dramas from the lists in this discussion as well, especially Japanese dramas where I'm years behind on what is trending.