 If you liked Death Note |  ...then you might like Tajuu Jinkaku Tantei Psycho |
Mind games, Machiavellian methods, and mass murders. If you found either of these titles interesting, you might want to also try out the other one since both involve unorthodox detectives hunting down serial killers. However, MPD Psycho is definitely not for the faint of heart with its sexual imagery, explicitly gory death scenes, and mentally unstable characters.
Both center around plots of psychological war-fare, an intelligent but slightly disturbed main character. If you like intense psychological drama and a hint of mystery these are right up your alley.
Both manga are dark suspense stories that deal with crime. They have similar thematic and artistic elements. MPD Psycho is a lot more violent than Death Note, but both have very dark storylines.
If talking about series with "hide&seek"/investigation themes, Death Note is a light version of MPD Psycho. Even so, if you liked one, you'll like the other. Each one have their own primary objectives: MPD is to be seen as very adult mangá; DN is to be seen as a "pre-adult" one?