I visited this WHS in March 2018. I spent more than half a day in this imperial city and really enjoyed entering the medina from one place and ending up in another while passing through several different passages, roads and alleys and sometimes getting lost.
I'm glad I hadn't visited Fes or Rabat before my visit to Meknes as my expectations would have been higher. The heart of Meknes is El Hedim (Lahdim) Square which in a way is a minor version of Marrakech's Jemaa el Fna. Tajines, lamps, craftware, clothes, toys, food, orange juice, etc. is sold in this square. Not only will you find sellers but also snake charmers, monkey trainers, acrobats, people with peacocks, camels, ostriches, reptiles or bird of prey to entertain locals and tourists alike for photo opportunities, horse-drawn carraiges, petit taxis, touts inviting people to eat or drink at their stalls, etc. The square is definitely not on the scale of Jemaa el Fna but nonetheless it is very enjoyable and very alive. The views of the square from the cafes with a terrace are mostly worth it for people-watching rather than the food itself.
The absolute highlight here is Bab Mansour which is best viewed in the late afternoon when the sun shines on the bright coloured zellij tiles. Directly opposite is the famous Dar Jamai Museum with its splendid exterior fountains. Even though it is worth visiting, don't expect too much if you've already visited other medersas or museums in the other imperial cities of Morocco. I also enjoyed visiting the granaries and the labyrinthine Kara prison if only to cool down from the scorching sun. The one thing not to miss inside the medina proper is the Medersa El Jadida (incorrectly named as Medersa Bouanania) which is considered to be one of the gems left by the Marinids (photo).
After visiting the medersa, I ended my visit with a gorgeous view of Meknes from Riad Selma's terrace, sipping mint tea and some delicious patisserie. All in all, I enjoyed my time here but overall I enjoyed all the other Moroccan medinas more.