Echoes of the Rising
Dungeon Masters are god, so when Dungeon Masters suck, everything sucks. All the above problems are so much worse when the Dungeon Master has them. A DM who’s spent too much on supplements often tries to cram them all into his/her campaign, which makes them an incoherent mess. Look, nobody ever says “That adventure was really entertaining because is was purchased and you included every elemental from the new Monster Manual.” And when a Dungeon Master hates a player in real life, it’s practically impossible to stay impartial when you have complete control over their character’s life. A DM who cares waaayy too much and always puts the rules over fun and story, or feels the need to check every rule at every juncture basically turns two-hour adventures into 16 hours of math homework.
But the biggest problem a DM can have is what I call Bastardosity. It’s like animosity, but with more dickishness in it. These DMs do nothing but try to kill characters and screw over players. Oh, there’s a time and place for that, and certainly, a flair for occasional cruelty is definitely an asset for any gamemaster. But we all know these DMs who feel they’re playing against the players, and the only way for them to “win” is when all the PCs are dead. A game where you never get to set out on the adventure because the tavernkeeper happens to be the brother of the lich-king you heard of 20 seconds ago and has poisoned all your drinks? That’s Bastardosity.