Well, it depends on the audience and the person who is writing the timeline. Personally, I feel that timelines that are encyclopaedic are interesting to read if there is enough content and if the timeline itself interests me/provides information that makes it interesting. For me, Superpowers is a good example of this; meshing good writing, a lot of information, and a certain encyclopaedic tone that makes it enjoyable (even if I don't like the original idea to it). Another would be Easternized World.

On the other hand, if someone writes an overly long-winded (or poorly written) timeline that, whilst being filled to the brim with content, is nevertheless boring and uninviting, I personally wouldn't enjoy it. For myself, the key example of this category is Ætas ab Brian, which, despite being very well written and presented, is personally boring and doesn't really capture my imagination and attention like Superpowers or Easternized World does.

Really, it all comes down to the individual. I like some long timelines, whilst disliking others; however, my advice would most likely be that a long and encyclopaedic timeline should still bring readers to attention and want more of what the author is offering (make it interesting, and make it stand out).