Sorry if I repeat, I'm trying this without reading so I'm not influenced.
A great DM ...
... focuses long term on the things the players show interest in. Even if the DM had plans for an undead invasion, if the players end up being privateers against the hobgoblin navy, the DM highlights that instead of forcing the campaign in directions they had planned.
A corollary to that is that a DM isn't afraid to change things that were set in their head but have not yet become canon in play.
... makes all of the characters and players feel special. Throw in chances for all characters to shine. And vary it up. This adventure they may be a lot of traps, but next adventure it's part of the rogue's background contacts, and in another it's an interest in the smith of the pair of magic daggers that they have been following up on.
... puts in choices, and makes them matter. This is both short term and long term. a "do you go left or right" in a dungeon where you have no information is not a meaningful choice.
... encourage some intra-party drama, but not let it get out of hand. PvP and severe disagreements are death knells, but some back-and-forth and differences of opinions leads to lots of good RP.
... rushes the boring and leaves time for the interesting. Mind you, interesting isn't always where you expect it. Had one game where the three pairs of PCs on watches overnight ended up in a few hours of great RP, with each pair of PCs in a different part of the room. Did any plot or adventuring happen during that time? Nope. Did the players have a great time? Yeap. And the flip side - if the players are bored with room 22 of your temple complex, plan your next dungeon more consolidated, perhaps using the Five Room Dungeon philosophy.
Building off of this, I like to let them have multiple different plot threads so they are choosing what they want to pursue next.
... keeps multiple campaign arcs and character arcs all alive. Not everything points to the same thing. Having this PC's search for her father, and that PC's hunted by the evil church he stole from, and this campaign arc about the dragons migrating away and that campaign arc about the political tensions that might errupt into war - it allows you to have a bunch of different types of adventures, and also lots of "ah ha" as they are doing something and then clues or actions pop up about others.
... knows their omniscient viewpoint highlights things to them. Clues that are obvious the the DM are not to the players. Put in any clue at least three times. If you expect themt o put A & B together and it's been two sessions and a real-life month between finding them, remind them. You aren't compromising your master plan, you're helping facilitate that half a day for the character is easier to remember then a month for the player.
... makes the world vibrant and dynamic. Vibrant - full of "that's awesome" and "I want to know more about that". Dynamic - make it living, breathing, things change both from their actions and outside them. Harking back to the multiple plots, some of the unfollowed ones advancing and some of them getting dealt with by other forces helps keep things feel alive. Heck, maybe that dungoen they were "saving for next level" got cleared out and now they have a rival band of adventurers.
... runs meaningful sessions. I had a DM once do a 7 session red herring quest. We hated it. Sure, there will be side quests and such, but let the PCs do things with meaning.
... have real risk. This is connected to meaningful sessions. This goes from the micro level of combat encounters with a real risk of death or other failure to the macro level of campaign arcs where you might not be able to stop that war from kicking off, or might even be the straw that broke the camel's back and caused it.
... aren't afraid to improvise and go off-script - and prepare so that they can do so.
... communicate well. Compare a DM who mumbles into his dice with downcast eyes behind his screen vs. one striding back and forth, voice and posture mimicking the NPC they are speaking as, or dramatically describing the hose getting pulled under by the bulette with a strong voice and dramatic pauses and volume shifts. But also the one who gives all the pertenint details the PCs would notice in a consise way vs. the one who leaves out the archers on the wall and only brings it up when the PCs decide to escalate to a fight and then need to retcon it.
... is having a good time as well.