Heat Guy J is very unrealistic. It is a ridiculous background to show off some bland, sympathetic characters. Even I like these characters, and I hate just about everything.
Why do I like this show so much more than so many other anime shows?
Because the characters have responsibilities.
The protagonist is probably 15 or 16; his tsundere love interest is similarly young. But both of them do grown-up jobs as police. If they were in high school, I would not have bothered to watch their slow but inevitable romance.
Conversely, Tatami Galaxy is critically acclaimed and artistically beautiful, and it doesn’t engage me. The characters are essentially infantilized, even though they are in college. Likewise, Shaft’s very popular Nisemonogatari did not win my loyalty, because the hero is infantilized and useless, but still gets to hang out with pretty girls despite his tremendous uselessness.
A lot of shows for teenage audiences suck because they show an unrealistic transition from infantilized passivity to responsible action. For boys, this often means, “You were stuck in a boring high school, but now you’ve been handed the keys to a mech, and the bad guys are invading in even bigger mechs.” For girls, this often means, “You were stuck in a boring high school, but now you’ve been handed a magical girl’s wand, and the bad guys are teleporting in from the Negaverse.” Two noteworthy shows that bring realism to infantilized passivity are Danshi Koukousei no Nichijou and Tonari no Seki-kun. The first confronts the passivity with humor and the second goes from passivity to active goofing off. Those two shows are watchable because they are entirely humor-based.
Note that “responsibilities” are sometimes more interesting when they are not confronted. Welcome to the NHK features a protagonist who fails to engage with his responsibilities. It’s a very interesting and engaging show, because it shows a realistic failure to behave like an adult. A much more cheerful show is Arslan Senki, in which the protagonist realistically fails to be a hero because he is a 14-year-old boy surrounded by highly competent adults. An example of Arslan’s failure is his misguided attempt to free slaves who are not psychologically prepared for freedom. Arslan fails for the right reasons, but he never fails too badly, and his companions always take care of him. Arslan also has the initiative to take action and act like an adult in many respects (e.g. basic riding and sword-fighting), so he’s not an entirely useless waste of space like Araragi Koyomi.