Making a megawad special?

I am considering making my own megawad. After scrapping so many projects when I lost hope, I want to make something good for the community to enjoy. I wanted to make a megawad but I want it to be special. I was thinking of making some weapons, music, cutscenes and other things to make it special. But, aside from that, I want to know what I could do to make my megawad unique and a step above typical doom mods.

Any help would be appreciated.

My first advice would be not to get fixated on "megawad" as a goal.

Harmony is a TC with 11 levels. Definitely special and remarkable, doesn't clear the "megawad threshold" (15 maps or more, according to the idgames archive requirement). Action Doom 2: Urban Brawl also has only 11 maps, and two of them are non-playable (TITLEMAP and CREDIT map). For more traditional gameplay, mods like Vanguard (13 maps) or Lunatic (5 maps), Arcadia (single map), Curse of D'Sparil (9 maps), Zen Dynamics (9 maps including two secret maps), etc. all have gotten awards and praise. So for a start, do focus on quality over quantity. It's not a problem if your mod ends up having just three maps if they're all good; but it is a problem if you have 32 maps and 29 of them are bad.