Played some Smash Wii U for the first time in years yesterday and had forgotten how much single player content that game has.
You have a very replayable Classic mode with random opponents and you can even use gold to increase difficulty and rewards. It might be a bit shorter than regular classic modes but it's infinitely more replayable.
You have all stars mode where you have to defeat every non mii fighter in the game.
You have events mode where you have to complete specific scenarios with special conditions.
You have Crazy Orders and Master Orders where you do endless amount of missions for rewards.
And then you have the trophy gathering mode and the training modes.
The 3DS version also has a lot of great single player content of it's own too like Smash Run, and it's own different version of classic mode.
I just really really hope they go all out on the single player portion of Smash ultimate too.
I'm a little worried that they're doing a story mode and that's it, leaving single player very bare bones compared to previous entries like so many other recent Nintendo games (Splatoon, Arms, Mario Tennis).
Classic Mode is already a step down (imo) since it's now just a set path of opponents pr character.
I know for the more competitive minded folks this doesn't matter at all but for me it's a big part of smash, I've always loved the amount of content in the games.