I like PDFs only because I can take them apart & rebuild them. I regularly make PDFs for my ebook reader (3.46"x4.57" pages with .02" margins; 10 pt Georgia font with 1.15 line spacing) because I know how to get them formatted the way I want, and I can't do that with ePub (because I am lazy and haven't figured out how). And I've got custom PDF settings for Feedbooks, because that way I can download several at once & combine them into one. But all commercially produced PDFs range from "mediocre" to "sucks rocks" on portable readers.

PDF is terrific for its original purpose: print-ready across multiple platforms from any machine. The bells and whistles on top of that are sometimes useful, sometimes a distraction; I can certainly understand the people who insist that PDF is "not an ebook format."