I don't get it either.
" its themed like the games"
that doesn't make it good, its just a festive pile of poop. I don't quite understand it, brawl isn't the best campaign but it was certainly a step up from melee.
Aside from the nightmarish enemies and generic levels, SSB makes for a weird platformer. It was frustrating fighting non-playable character enemies considering how combat wasn't balanced for that type of gameplay. It also sucked to get knocked around on this levels since the camera wouldn't zoom out that far most of the time. Running around with high damage was just a pain.
Melee's adventure mode still consisted of mostly traditional fights. It didn't need to stretch itself out to a ridiculous degree like The Great Maze from SSE. Even if I liked the rest of SSE, it would've been boring running back through similar looking areas. It was like that Zelda triforce dungeon from Melee, but 100x worse.
Some of the cutscenes and scenarios for SSE were neat, but half of them revolved around original (nightmarish) enemies and the creepy/weird Brawl universe where the characters know they're trophies and fight for the entertainment of faceless crowds, and Dedede has medals that turn trophies back into people... ugh.
Having Nintendo themes in a game built on the concept of fanservice is a big deal. If there's going to be considerable story elements to the adventure mode, keep it shorter and sweeter like in Melee. If you go all out, let me see familiar heroes team up to fight familiar villains with a story that just mixes established Nintendo universes, then at the end you can introduce the new surprise villain (which should be the kid from SSB64 playing make believe, something far less creepy than whatever the fuck Tabuu was).
This level of Nintendo crossover doesn't happen anywhere else; we don't need a new universe and new enemies to make it special. Just seeing Star Fox team up with Samus is enough to make it cool. There's so much source material for sora to pull from an da lot of characters, enemies and places fans would want to see in the game. No one voted for this thing on any fan poll: