A lot of incremental games I see are in perpetual development. They are never truly finished, the developer always promises that another content update is around the corner. And those content updates get released, and the games eventually get really big. They grow to have prestige layers approaching the double digits, or months of content, or twenty-something interconnected systems, or whatever else it is that makes a game big.
Now, I want to like these games. Progress is at the core of incremental games, and appreciating the amount of progress you've made since you started is something I think long-term incrementals can and should excel best at. Unfortunately, I find that most long-term incrementals are not designed such that you can appreciate all the progress you've made. At most, I can only compare myself today to myself a few days ago. It feels like many games would be better served if they were split into smaller games. At some point you're just adding content for its own sake.
I want to know and let other people know possible ways of solving this issue, although I'm ultimately not sure whether it's even possible to solve.
I'll try to help by citing what I believe to be a positive example:
Evolve Idle is a game about growing civilizations. It is a tedious game. A lot of the game is spent repeating the same content over and over again for minuscule boosts. The amount of time you have to wait between actions increases as you progress further in the game. And if you stick to the areas of the game where the intervals get shorter, they eventually get either bored or exhausted with how much you have to monitor the game.
But the game is also really expansive. Each little boost is a tiny bit more progress into allowing your civilizations to perform greater feats. Eventually your civilization gets to ascend to a higher plane of existence. I ended my playthrough there, but that is far from the end. The reason I ended it there was that I thought it was a fitting end. It was the best ending I could think of for a civilization, and much of the content after that was mostly just reaching endings I considered to be worse and then doing them under more difficult conditions. There was also the fact that I had been exposed to third-party automation scripts for the game and the progress I saw late-game people using these scripts ruined my sense of scale.
... that's a long example. It would be a longer, but I'm sleepy.
I've discussed this topic and levied criticisms at common issues I see in this genre in an article called What is Content?. Essentially, I think it's better to have planned out the scope of the game in advance (as I've done for gamedev tree, advent incremental, and Kronos), so that the game feels like it has a proper end. It also sidesteps the issue of having new layers outright replace the earlier gameplay rather than extend it, as is common in games that keep asking themselves what to add next. Basically, planning makes better games.