Hi Necro, been a while!
I have the game, yes, and started my playthrough earlier this week. I can understand casually dropping the first one at some point since it's so long, although I didn't really mind myself. Finishing it before jumping in the sequel isn't necessary, though, at least for what I've seen so far. Some characters meet up again and will say something like "Hey, it's you! Nice to you see again after the last incident!", but that's pretty much as far as it seems to go plot-wise.
I mostly expected a cash-in sequel, since developing all these assets for the first one must have been costly, but I've been pleasently surprised. Many characters return, although several pairings are shuffled around. New attacks have been added into the mix so the animations don't go too stale. Several music tracks are back, but every single piece appears to have been remixed anew (!!). An item shop is now available, adding an extra layer of strategy to your pre-round planning.
It's very similar to the first one, obviously, yet they change things around enough to make it worth it, in my opinion. If you have any doubts, they released a demo on the 3DS eShop, so you can judge by yourself! 
The admin formerly known as Dr. Cossack.
I post musings, images and nonsense on Tumblr! I play games on Steam! Add me on either/both, and don't hesitate to ask if you want to play something with me!
"There are only three things certain in life: Death, taxes, and Teej's obsessions." ~ RisingDragon (still true in 2019!)