Combine the uncombinable - is the main idea of those two mangas. Authors played with one of the most well-known and old human stereotype of form and content. What if something is not what it seems? What if someone who looks evil is really an angel or vice versa. Almost all comedy situations in those mangas based on this contrast between the true self of our heroes and their appearance.
Besides the art is pretty similar too. It looks a little bit creepy at first sight but it fits the atmosphere perfectly.
The comedy of Detroit Metal City continues in Minna Esperanto da yo, and with a continuous story as well! All the awkward and silly characters and situation you love is back, except for the metal. Which is kind of ok.
Kyou Kara Hitman and Detroit Metal City are both episodic gag mangas where the MC have a secret identity. Every chapter in both mangas is about how the MC have to take care not to be caught by the people who dont know about the secret identity and makes jokes about this. In Kyou Kara Hitman the rape and killing that is talked about in Detroit Metal City take place in small doses, which can be quite refreshing after 10 volumes of Detroit Metal City.
Solanin is a very down-to-earth slice-of-life story whereas DMC tends toward vulgar slapstick, but at their basest levels they're both about using a passion for music and a place in a hastily composed band to follow dreams and to make the best of and/or overcome a less than ideal situation.
Detroit Metal City and Devil Ecstacy have the similar kind of feeling to it, the humor and drawing style, though Devil Ecstacy is totally NSFW. Both have this kind of slap-stick comedy that is way over the top, and challenges what you feel is appropriate to laugh at.
Both of these comedies typically use mature themes as a means of generating humour. Azazel-san features copious depictions of violence and scat. DMC also makes references to violence, as well as concepts related to lust (particularly BDSM).
Admittedly a vulgar death metal band and a group of dayglo-haired high school girls don't have much in common, but both series do have a similar strange, quirky, oddly endearing sense of humour and not much in the way of any overarching plot structure.