If you're looking for manga similar to Doraemon (Taiyou MATSUMOTO), you might like these titles. All recommendations are made by Anime-Planet users like you!
The world is stunned when one of the seven greatest robots on earth, the universally beloved Mont Blanc, is found murdered with his head desecrated with makeshift horns. To confound the situation, the renowned robot rights activist Bernard Lanke is also killed and mutilated in a similar manner. Eager to solve these puzzles, Europol German Division employs the help of detective Gesicht, an advanced robot who has cracked some of the most difficult cases known to man. But no sooner has Gesicht received his orders when the robot North No. 2 meets his end along with the creator of the international robot laws, Junichiro Tasaki. While society struggles to come to terms with these incredible events, one thing becomes clear to Gesicht: someone is targeting all of the world’s most powerful robots and it is only a matter of time before they get to him…
Both these manga take an extremely popular classic children's series (Astro Boy and Doraemon), and repurpose them for a mature, seinen audience. Though that sounds pretty gimmicky, it works since Urusawa and Matsumoto are masters of their genre (though this isn't Matsumoto's best, by a longshot). The plots (and lengths) of both are completely different, but if you liked the concept of seinen-ification in one, check out the other.