Without reading that thread, I think I was using them as an example of old shows for the nostalgia argument (I did like them as a kid). But like I said, taste change over time. I used to like the 80s Ninja Turtles show too. Now I most certainly do not. Though I should clarify I don't hate those shows, and may even find some of them enjoyable, they're not something I have any interest in either (I'll touch on that in the below Simpsons comment)
It's kind of the opposite for me. If I can skip an episode and miss nothing, then it doesn't interest me that much and comes off as filler.
Usually that's when the show based on a comic catches up to it and has to wait for the comic to get ahead again. Otherwise, shows that wait to make an adaption tend to have little to no filler (like Death Note). Though I think proportionately JLU has more filler than plot (if we're saying the Cadmus stuff was the 'main storyline', where even drawn-out shows like Naruto and it's filler saga have more plot than JLU did.
I believe they did give a reason that the Millennium Puzzle had to be won in a game and couldn't be taken by force (as far as why Pegasus didn't do that). Then again, you could also ask why the cops/Batman never kill the Joker, or why they don't build a boat on Gilligan's Island when they can make radios and other more advanced stuff.
Maybe not 'bad', but not something I would go out of my way to watch. I mean, I can watch Spongebob and other similar shows, and laugh and enjoy them, but I would do that only if it's just something to watch while I'm eating or working. I'd never break a gaming session or something to go catch the latest Chowder, since there's no story or plot to persuade me to do so. I only watch TV for about 30 minutes a week right now.
Usually it's more fleshed out, and more can happen. In a single episode, things tend to resolve within 30 minutes or less. But in a story spanning an entire series a lot of things can happen: important characters can be killed off, where as killing of a one-episode character doesn't have as much impact as a character who's been there from the beginning. I like seeing how the plot changes and escalates up to a climax, and the outcome of that struggle. If I'm just watching Superman beating up different thugs week after week, it's just not as interesting as a hero struggling against a goal for the whole series with plenty of twists and turns in the storyline along the way. But, say, Mega Man Star Force, which shows Geo and Omega-Xis' struggle against the FMians invading Earth, there's a lot more to it than that. Each episode contributes to that overall plot, and things start getting really focused when the threat becomes more serious over time and more revelations about the characters and plot are revealed. The US has a few shows like that, but not as many as they do in the vein of Superman and the like
I've heard that before in the Spectacular Spider-Man thread about a show being about a character's life, and while I suppose it technically counts as a thematic for the show, I don't really consider it to be in the same vein of an actual storyline, like Monster or Iron Man. I think thematic and story, while they can be connected, are fundamentally separate entities. For example, Iron Man has a coming-of-age thematic as well, but it also has the whole plotline of Tony finding the five Mandarin rings to follow in his father's legacy and stop Stane from destroying Stark International.