 If you liked Monster |  ...then you might like Homunculus |
Similar in pace, short fast chapters. Both have lots of mystery and deal with psychological themes.
Both anime follow the same protagonist pattern: middle-aged man at top of his career suddenly having his world turned upside down for reasons they cannot comprehend. Then there is a strong component of introspection and personal journey with touches of insanity. They both present an engaging story even though Homunculus tends to be more on the borderline disturbing side, with a lot of wtf moments. Lastly, the drawings and tables are brilliant for both manga and somewhat feel similar, so tuck in and enjoy the ride