I've been to the Sistine Chapel, and yes it has a lovely ceiling, but it's also jammed full of other tourists who are also craning their necks and not looking where they're going.

While the Vatican has a lot more loot and bling to look at, I'd say looking at the pictures on https://en.wikipedia.org/wiki/Gallery_of_the_Sistine_Chapel_... is the superior experience.

The same goes for the Mona Lisa, which is the least interesting painting in the Louvre. Either see it in a crowded room full of tourists, behind a glass case, or see every last brushstroke at https://en.wikipedia.org/wiki/Mona_Lisa (7k x 11k pixels in uniform lighting)

Personally I liked seeing the brickwork of St. Peter's dome more, but each to their own.