A recent trip to the opera with my mother exposed a glaring lack in my education

I know nothing at all about opera. I could name maybe three operas if I tried really hard (and one of them is Don Giovanni, which I remember mostly because I had a small Mozart phobia as a child thanks largely to my dad playing this record). It simply never crossed my path and I know nothing about it.
So I went home, looked up the opera we watched on Wikipedia, and feel like I have a pretty good overview. I don't really desire to know more than what Wikipedia told me. I did feel a little like I should plug this gap in my knowledge, but them, there are lots of things I don't know about. History is another area in which I am weak, and when I trolled Project Gutenberg for some books on that, I came across five-volume biographies, a 32-volume history of Canada (and it only goes up to the building of the railroads---imagine how long it would be if we carried it through to the present day!) and what appears to be a diary that Pepys kept for several decades. Does anybody really need that much information about any of these subjects? Isn't it just a little too much? What would I gain from a five-volume biography that I could not get from reading something shorter?
I guess I feel like there is just too much out there I want to read to spend years of reading time reading about what Pepys had for breakfast. Am I missing something here?