One of the players is marginally concerned with plot, so I presented him with the "round up magic items for coin" hook, and that seemed sufficient. The others just wanted to go in and kill stuff, loot, and level up.
I'm more used to running dungeons that have interesting challenges in most areas. Whether they are combats to win, NPCs to negotiate with, secrets to explore, traps to avoid, or even an interesting feature to discover. Mad Mage seems about 50% empty, with many rooms "the only thing of interest in this 60 ft. area is a frayed coil of rope."
Sorry to hear you've been having some issues with it!
I think just playing the DotMM as a mega dungeon with the sore aim of killing monsters, looting rooms is unfortunately going to get old fast. Instead, think of the mega dungeon as a campaign setting in itself, with the inhabitants themselves serving as additional plot hooks. Meaning DotMM will need to be thought of as a dynamic world in itself rather than just a mega dungeon.
Give these creatures reasons for wanting to kill the PCs, reasons for talking to the PCs instead. Even a monster may just want help, in defending its brethren from things worse in the dungeon, or it may want food in exchange for simple passage, as examples.
You could also organise the inhabitants into factions, meaning a defeat of a certain group could mean ascendencies in power of another group, which means this group might make forays beyond the boundaries of their initial territory into other regions of the dungeon, or it could send the shockwaves of a power vacuum throughout the dungeon as a whole.
Which means you may need to give each inhabitant of the dungeon a goal, with motivations and relationships.
Make the dungeon dynamic, there's bound to random monster encounters roaming about.
Hopefully random generators can also help with this, because all of this sounds like extra work, but it'll be worth it because the inhabitants themselves, the features of the rooms are all already written for you. Best of luck.