This question is kind of wonky to start with. (To OP - this is not a slam against you or your question please read on)
So far I can agree with any response here so far - after DMing campaigns for about 23 yrs, let me start by saying that a well run campaign, adventure, night of playing is neither, both and somewhere in between your stated question.
During the creation process a DM needs to be Lawful uncaring in that the setting (used from here on may mean world, dungeon, or any other part of campaign, scenario creation) is made in such a way as to be believable (whether fantastic or realistic), cohesive and alive.
During the tweaking phase the DM should be adversarial in nature - individual challenges need to be tough, innovative and thought out from the perspective of the monsters, NPCs or situation in question. If the party has all fire magic the DM should NOT put in creatures that are immune to fire just to nerf them. However if the adventure takes place in the shadow of a volcano, then having those monsters around is probably not out of touch with reality. Traps should be believable and deadly, they are traps, they are designed to kill, maim and injure intruders, not just annoy and delay. That being said, I believe that many traps that are created inside the RPG genre are just unbelievable and frankly crappy (I know I've created a few doozies in my time). And even the lowly kobold or goblin should defend their homes as if they are defending their homes (for a unique perspective read
this comic from the beginning), they should probably act like it.
Then during play the DM should be all of the above and more - innovative in trying to have the monster defeat the party, helpful when the party contacts NPCs for help, neutral during rulings and above all else FAIR. Be open to ideas, reward out of the box thinking, role play and strategy; punish ignorance, stupidity and laziness. The even handed situation created will be fun. Power gamers, actors, newbies, hangers-on, recreational gamers, armchair generals and devout grognards will find your table to be JUST what they were looking for.