Hard to say, depending on where we treat the cutoff point. For series that are OK/fine but not at the level where they can be viewed as good, probably Zeta Gundam as some of its plot lines and character motivations can be pretty flimsy, but the general premise and most pivotal story beats are fantastic. This is what the Star Wars sequel trilogy should've been, rather than the fan fiction woke shitshow we got.
For anime/manga that I like but are average/mediocre, probably Kinnikuman. It has a lot of messy plot devices such as power of friendship and several retcons as well as some parts that are needlessly devoid of logic, but I can't help but appreciate the characterisation, creative designs and the manly aspect of it that are missing from modern Shonen that attempt the same thing.
Moving on to series that are outright bad, I'll take the cheap route and say any dubbed Hentai as the dialogue is always comedic gold, particularly this one:
[youtube]nLmsVBgZiak[/youtube]
I could say Ghost Stories due to its dub or Inferno Cop, but the former was made specifically to make a bad series entertaining and the latter was intended as being as low quality as possible for the comedic factor, so it's a bit unfair to include them.
That's without factoring in certain additions to select anime/manga. My choice for any of those categories could change depending on if I lump the post-timeskip material into Hokuto no Ken or post-Z material into Dragon Ball. The former is pretty arguable how good it'd be if including Part 2 depending on how damaging you consider it to the overall quality of the series, whilst the latter is definitely pushed into the bad category when factoring in GT and (especially) Super ruining what was good about it.
) of this song works against it. In particular, the change in tone around 12m - 18m is so stark that it may as well have just been a different track altogether or used for a different song. It also doesn't help that the intro is far too slow, with the song only really coming into gear after the first 2 minutes.
