You make a new entry in a series, you're gonna be compared to the other entries in the series. Prequel, sequel, reboot, next issue of a comic book, latest episode of the latest season of your favorite TV show, E3 presentations, NBA seasons, meals at a restaurant, everything. Whether you're aware of it or not. You analyze what you're seeing/consuming and you articulate what you like or didn't like about it, often comparing it to previous experiences you had. "Wasn't as good as the first movie" "Best one yet!" "Did you do something with the sauce? Spicier then it used to be" "We're never getting into the damn playoffs again :/". This happens everywhere, all the time, constantly. It's human nature.
A reboot is still another entry in the series. It will be compared to other entries in the series. Some fans do it favorably(Ezekiel just can't seem to get enough of it and updates us whenever NT lets a fart that sounds like DmC info), others do not. We are reacting to changes in a new entry to something we are a fan of. Being a reboot does not exempt it from criticism, like the 30 fps or the character design.