Yes, Japanese dramas are different than Korean and some of them are too fast-paced. But recently I started watching more of them and I really enjoyed
Atashinchi no Danshi.
Now back to the Korean dramas.
If you like action and mystery I recommend
Vampire Prosecutor, especially second season which was really amazing and last few episodes were really intense.
It was never boring when I watched
Shut Up: Flower Boy Band. If you like music dramas try that one.
As for the rom-com genre I'm not really sure but you can check out
My Girlfriend is a Gumiho. I enjoyed very much
City Hall but some people like to avoid political themes which is unfortunate since this is a very good drama.