I want to add, season 3 got very, very unlucky. Most people despise it because of the events that happened immediately following its finish, and the very large hiatus between s3 and s4. Season 3 was cut short, had a very obviously rushed finale that turned one of the shows most beloved characters into something else, and at the time it seemed like it would drastically change how the show worked. So you had a rushed finale, twilicorn, a shortened season compared to the other two, and then you had the massive crap storm that rocked the fandom, Equstria Girls. This added on top of a short season, a major (at the time) change to a main character. And to add to all of it, the long wait between season only let the season be very over analyzed, and with nothing to keep most of the fandom occupied, they just dwelt on season 3. How short it was compared to one and two, how they changed twilight into a alicorn, how on top of that they added EqG. This series of events led alot of people to forget about the good the season did have, and rather focus on the almost over shadowing negativity that followed it.