So I just finished watching Golden Boy (1995), since I was curious about it and was very often recommended on various lists of retro anime to watch. It turns out that the show is obnoxiously horny, reaching "I can't believe it's not Hentai" levels in Episode 5 and that the show revolves around this seemingly incompetent dude that basically thinks with his genitals and always ends up getting the girl. The comedy is also basically 90% sexual and with such a setup, you can't really expect much else than objectification of women.
The animation quality is neat and the ED song is catchy though. 5,5/10
The above description might sound familiar if you've watched Great Teacher Onizuka (1999), which is similar in concept, except it includes a pretty good story and interesting characters. Unfortunately, it also is obnoxiously horny (which makes it creepier than Golden Boy due to the setting of GTO), is very ableist towards one of the students of Onizuka's to the point where episodes centered around them become unwatchable if you have a single ounce of liberatory ideology in your head and the show has some really bad filler episodes.
7/10? Sure. 8,69/10, like the MAL rating says? No chance in hell.
I don't really have examples of underrated shows or manga that are noteworthy enough to warrant me complaining about unfortunately.
This is a personal thing I assume but I could never get into Gintama and would probably give it 5s if I could actually get through a season. But Gintama fans give it nothing but 10/10 non stop so it's always completely overrated.
Code Geass is very overrated.
Kimetsu no Yaiba is also extremely overrated. Not a bad show though, I don't really dislike it but it's also pretty throwaway shounen.