The Sistine Chapel is lovely. I don't discount checking a box to say that you've been there. But while you are there, explore more of the vatican museum. There are countless artifacts there that would be the centerpieces of less important museums, but in the context of that museum, they might go unnoticed in a corner. I find this true of tourism in general. 80-95% of the crowds go to 5-20% of the things to do. In the Louvre, it's the Mona Lisa. In the Vatican it's the sistine chapel. Meanwhile there are museums filled with pieces that would probably auction for 8-9 digits, but for whatever reasons, are not well known to the general public and therefore don't get the attention. No one is taking selfies of themselves next to the 17th most valuable painting in the Louvre (much more so the 100th most valuable piece, which is still extremely valuable), but I assure you that the quality of the work is every bit as fantastic as the most famous ones.