So I think we've established that if it doesn't
feel like filler content, then either you did filler content right, or it doesn't count as filler content in the first place.
I'm going to look at what
@CardinalCoder64 defined as mechanical filler content, as I think visual filler content is almost always totally fine, since it doesn't waste the player's time in any way.
And I think that's the trick: bad filler content makes the player feel like they wasted time. And so, I think instead of trying to specifically determine how to use good/bad filler content, I think we should focus on how to not waste the player's time, with anything, filler content or otherwise. What feels like a waste of time when you're playing a game?
Note: Most of the games I reference are Zelda games (especially Breath of the Wild, since I've been playing that reccently). Mostly this is because more than half the games I've played are Zelda games...
Here are a few pieces to that:
-Avoid Repetition: When the player is doing the same thing over and over again, eventually that will feel like a waste of time. Now, depending on how much fun that is, what the purpose for doing it is, how often that happens, and how much variation you add, you can sometimes repeat something a lot, but you need to be careful.
In Puzzle Quest, doing the combat puzzles is not a waste of time, because it's core to the game-play experience, and it's fun to do, even though you do the same type of puzzle every single time. (That is, assuming you like games like that. If not, you didn't play Puzzle Quest). But in MMORPG's, you often end up grinding enemies, the same monsters over and over, this ends up feeling like a waste of time because you
could be doing something else, but you
have to grind.
-Consider the Purpose: One of the most important parts to any content in your game is
why. What is the point of doing something? Sometimes it's just fun. (If you're content
isn't fun, you might have a problem...) But beyond that, something feels like wasted time if there's no point. Even if something is super fun, if you finish and you think, "Huh? Why did I have to do that?", then it probably feels like a waste of time. For some people, this purpose
can be advancing the plot (Like many in many RPGs), but this falls flat really quickly. The best way though, is in-game rewards that are actually significant, like cool items, access to new areas, actual changes to the game world, new abilities, life boosts, basically, significant advances to the playing experience. Rewards in the form of currency, XP, or achievements should be very limited, I think, or else combined with those other things.
I couldn't think of any games I've played that do this right all the time. Zelda is good sometimes, where the required main quests give you useful items, like the hookshot. Or in BotW where killing monster bases is always useful because your weapons break and you always need new weapons/food. On the other hand, Zelda side-quests, while in some games they give you better quivers or heart pieces (which are nice), they also (especially BotW) just give you stupid rupees you don't need. (BotW is the best at this so far, because rupees don't drop naturally, but still... I DON'T NEED 300 MORE RUPEES!)
In a sense, something doesn't feel like a waste of time if it feels useful or productive. Kind of the definition of that.
-Make things optional: Producers might not like this, because in some way, you just made the game shorter. But, at the same time, the game isn't any smaller
and it's better for it. The best way to prevent something from being a waste of time is making it optional. Then it's there for the players who
want to do it, and everyone else just skips it. This is better for everybody except the people who want to say the game is 200 hours long, and people like Jirard the Completionist*.
Very rarely does anybody thing something is a waste of time if you don't have to do it. As much as I complained about the mini-games in Zelda, it doesn't really matter because I just skip them most of the time. And if it looks fun, I'll do it anyways. And nobody was supposed to find all 900 korok seeds in BotW, I think I've gotten around 60, and that seemed like enough for me. So you could argue that the korok seeds were filler content, and, yeah... but no one really cares. Except Jirard.
There's more, but I'm out of time for now. The point is: how do we not waste the player's time? Filler content itself is not really the issue I think.
*As a side note, a 100% completion bonus should be incorporated I think, all the time, even if it's really lame... Also, post-game save, so you can keep playing after you finished. Unlike the bulk of the Zelda games. Actually, two of the Paper Mario games have extra quests to do only
after you played the game.