So far the only long form series of LNs I've attempted was Index. I tried binge reading all of OT and while I didn't really notice a dip in its quality, I felt myself getting burnt out by volume 16. I haven't really picked it back up since. That's more on me than it is with the work.
Like most things, there will be high points and low points for such series, but as long as a positive average is maintained, I'm down.
The next longest series I'm familiar with would be Realist Hero. The first 4 volumes are great because there was a narrative that was meant to be told all throughout. When that arc ended, volume 5 felt like it was tacked on. Fortunately, it picks back up afterward and has been pretty good again.
Where was I going with this? I forget.
tl;dr I can accept dips in quality now and then as long as overall it's good.
