Almost all of the revelations of long-standing Bionicle mysteries that I've hated were revealed for the sake of revealing them, rather than because they had any relevance to the plot at the time. The ones that were relevant to the plot, I did like.
Where the Bohrok came from -> Avotoran? Possibly the single plot development I hate the most of all of Bionicle. Was it revealed through some actual element of 2008's plot? No, the Nuva just randomly came upon some thrashing Avotoran for the sake of revealing where Bohrok came from. Origin of the Exo-Toa -> they're just a commonplace element of Makuta's armies? Boring. Did Exo-Toa have anything to do with 2005, even its backstory? Nope. Just thrown in there. Give me time and I'll probably come up with more of these.
In contrast: What does Mata Nui look like physically -> He's the entire universe? One of the most dramatic, well-executed animations from all of Bionicle, and kind of central to the plot at the moment, which was the awakening of the Great Spirit.
So, moral of the story: if you set something up as a grand mystery, don't reveal the answer in an aside. Unveil it in a way appropriate to how mysterious it was.
I'd append this with something about "in my opinion" but I think this is generally regarded as just common sense in the realm of writing. Your feelings about the revelations named may vary, however.