Yeah, there was a lot of filler in it.
What I'd want from a new Adventure Mode would be every stage to be a full side-scrolling level like the ones Mario, Zelda, F-Zero, Metroid, and Ice Climber got in Melee. Obviously they wouldn't be able to do it for every series, since there's so many now, but I think limiting it to the franchises from the original Smash 64 would be reasonable.
Actually I think it would be more than feasible to go all out with it in the next iteration of Smash.
Especially if they don't build a new game from the ground up and use Smash 4 as a base.
I posted a mock-up menu tab of it before, but I had this idea for a Smash 4 Adventure Mode before it came out, called "Super Smash World" that would be a fusion of Melee's Adventure Mode and SSE in terms of how it worked, while also taking advantage of Smash 4's customisation elements.
The set up would be simple in that the story involves the characters being at some party or tournament or something held by Master Hand, but then Crazy Hand swoops in and turns everyone into trophies and makes off with the trophies. However, two characters will manage to evade being turned into a trophy and kidnapped. Who will do so is a choice the player gets to make when creating their save file (this is to avoid the issue of players having to play through hours of the mode just to play as their favourites). Beyond that there is no real story to it. It's like a typical Mario game, you are given a motivation and you just play through the game. However, the levels would have things going on in the background to make them feel alive and make it seem like things are happening in the various worlds (e.g. a Peach's Castle level would feature a bunch of panicking Toads trying to deal with Goombas and Koopas).
You would then have a World Map akin to Super Mario 3D World, and you basically just make your way through levels themed after the various games (games with multiple reps get an equivalent amount of stages), with the different characters being scattered across the levels. Most levels end with the character being released from their trophy, but they are corrupted and you have to fight them. Defeat them to make them normal again, and then you recruit them as a party member. You can also use equipment on characters to make them stronger and there would be a much more generous limit on equipment compared to the normal game. There would also be a shop for equipment similar to Kid Icarus: Uprising's weapon shop.
Levels would play out very much like SSE, but each level has it's own unique elements and enemies match their world theme. There would also be collectibles in every level, Smash Run power-ups, etc.
There would also be boss battles, some secret, some not. These would be a mix of Subspace bosses and bosses from the game worlds.
I was also thinking Event Mode could be grouped in with this, having events dotted around the map besides the levels, but you need to have the appropriate characters in your party to tackle them.
It's not gonna happen as DLC for this game obviously, but I'd love something like this for the next game. I would also envision it having both local and online co-op.