The piling on and piling on of meta knowledge is what I object to. It goes against everything 5e was designed for, streamlined ease of rulings at the table and DM empowerment. I play a PFS druid, and the amount of knowledge outside Core I found I was expected to know about animal companions was annoying. Books I had never heard of and didn't own, changes to what was in the Core, and a gazillion FAQ questions to wade through to find the info on it that I needed, on a website I don't normally visit. It made everything a million times more complicated than it needed to be.