Is this drama worth to watch?
There are definitely better ones but if you just want to enjoy the performance of the actors then yes it's worth it.

Is it predictable? Overall yes.
There are 3 investigations. The plot of the first two have been seen over and over with a banal approach and serve as an introduction to the last one. The last case is more promising as it digs into Ryu Soo Yeol's past. Nevertheless, there are some silly flaws, the transition between episodes 8 and 9 is too abrupt, the main thread is too superficial. There is also the eternal problem of the one-man hero in crime series. As for the villain, he is cruelly uncharismatic and turns from a smart guy to an idiot in the space of an episode.

Is it easy to watch?
Yes, it's quite well paced and the actors are excellent. It's not very boring but it's not overwhelming either.

Warning: The characters keep yelling at each other throughout the drama.

Final note: 7.8 /10