I like them in that they give you a lot of levers to pull on to mix up class balance. Adding more short rests (and more encounters) favours Fighters, Monks and Warlocks. Subtracting encounters (and increasing difficulty) favours Paladins and full Casters. You can move the spotlight around the group, and play with class balance easy, and stop things feeling too samey.
I dislike them because I have to constantly come up with Doom clocks and other contrivances as invisibly as I can to stop nova strikes and to maintain 5E's class balance. That can get tiring and it requires you to frame your adventures (and adventuring days) appropriately.
I'd really like encounters to be balanced more around the individual encounter. Removing as many daily resources as possible, and having spells, combat manoeuvres etc all function like Tome of Battle in 3.5, or force powers in SWSE; per encounter abilities.
That's just me though probably.
Wait till those DMs deal with 20th level+ PCs. Those guys most closely resemble the Avengers. Everyone can fly (or teleport), shoot lighting from their fingertips, fall from the moon and survive, mentally communicate with each other, breath water, call down meteors, or take down a T-rex with nothing more than a butter knife.