Pinning down what determines the quality of a multiplayer mod is a bit of a unique beast. Whether a mod is technically good or bad is kind of irrelevant; you can be technically innovative, you can do new gameplay concepts, you can make all sorts of custom content, but in the end what matters is...whether people play it and like playing it. Community reception can make or break a mod. Sometimes they can be a resort for occasional weekend visits (WhoDunIt, Push, Ghouls vs. Humans), sometimes they can drift away from the mainland and sustain its own population for years (Mega Man 8-Bit DM). And then there's QCDE, which caused a plate tectonic shift so massive that it left us with an entire separate continent on which a new civilization sprung into existence.
Wait... King Reol? Like REoL TOUGH King REoL?
It's nigh-impossible to oversell what DBThanatos and Michaelis managed to pull off with QCDE. They've been partners-in-crime since their nearly decade-old crazy resource-hoarding simulator Aeons of Death (the word crime isn't used lightly here) and two years ago their team won a Cacoward for D4D, the conversion/demake of Doom 2016 in GZDoom. Well, they've outdone themselves this time, because QCDE isn't merely another zeitgeist-capturing mod/conversion. The main reason why it gets a Cacoward - and why there is no other MP Cacoward this year - is because QCDE by and far outshines every other multiplayer effort that has come through this year.
It's no secret that QCDE's base gameplay takes unapologetic inspiration from the fancy new id game that happens to have a similar name. You've got a set of different characters with different abilities, you've got a set of different weapons, you've got a set of different maps, go wild. You select your character, your opponent(s) selects theirs, and you all start jumping around wildly while shooting at each other. But, as Samsara proved years ago, that's really all you need to make something fun - and if you give the players something to build off, you can watch it expand. And expand it has. QCDE has spread far and wide, spawning a huge variety of different sub-mods, a completely separate community, dedicated streamed tournaments with cash prizes, and even a metal album. A metal album? Now that's something not a lot of other mods can brag about.
Having fun with your mates is ultimately an extremely simple concept, and QCDE captures the old days of the LAN parties where everyone was yelling at each other, the spectacle of watching the Quakecon finales, all in a free mod for Doom. But you don't need to make something complicated to be fun, you just have to engage people. Nothing else in 2018 has come close to the community-shaking that QCDE has, and it's going to be around for years in the future.