Main number one issue with the SSE: It tries to tell a complex story involving give or take 31 people, WITH NO DIALOGUE!
It's next to impossible to follow a story where no one speaks, unless it's like a 1900's comedy or something, but something like the SSE? Imagine the Harry Potters films completely silent, no subtitles.
Without the help of the Dojo, you'd never be able to figure how and why Snake got on the Halberd, or what was going on with Mr. G&W, or what Tabuu was, etc etc.. That's why people don't get the story. It is the WORST told story I've ever seen. That is, worst presented story.
Also, some plot points don't get properly followed up on, like the lack of a Ness/Lucas reunion scene, no explanation to a certain blue guy coming up so damn late or where he was to start, or three characters not showing up at all..
The GAMEPLAY was fine to me, but it's let down by the multitude of generic enemies and boring locale. Extra annoying considering the first few bosses including Petey/Porky/Rayquaza, and then the game throwing it out the window and adding crap like Duon. Correct me if i'm wrong, but only 5 bosses in the mode are Nintendo related (The before mentioned 3, and Ridley and Meta Ridley)
My opinion: There's some good, like the many collectibles are fun to look for, but there's many fatal flaws. I don't think it's the worst thing to ever happen, but I do think it was poorly executed. I don't want to see it back, it would be even more a headache with a bigger roster, and the lack of a new Dojo.