Loading times are a bit on the long side, especially during Classic mode when it's loading the "team" enemies while you're walking around waiting for them to drop.
I finished SSE two days ago with a friend, we completed it on Hard. The last boss was pretty difficult but mainly because my friend couldn't dodge that OHKO attack, so he kept losing lives. On the go we managed to beat him in I was left with Ike and managed to get 2 smashes in, only needed one hit after that which I also managed to land after a few tense moments.
Beating it unlocked a whole bunch of stuff, but I still have three characters left,