Just imagine what we would have missed if the show had lasted just 3 seasons All those great episodes like The Perfect Pear, Amending Fences, Crusaders of the Lost Mark, Sounds of Silence, A Hearth's Warming Tail, Twilight's Kingdom and so many more.
We would never have met Starlight, Maud, Autumn Blaze, Thorax, Ember, the Young Six and Flurry Heart. We would never have seen Discord's transition into a hilarious comedy character or Daring Do as a real-world character or seen Twilight's Castle and the Cutie Map, the School of Friendship, The Changeling Kingdom, the Kirin village and Starlight and Trixie's friendship.
I've heard that a huge number of fans jumped ship after season 3. They don't know what they missed!