I think the weak DLC selection (at least for me). Banjo was cool and all... but the first Fighters Pass was really third party focused - and I felt not in the good way. The focus was clearly on getting big icons together, and for me, Smash is a celebration of Nintendo history. I felt like a few third party characters "closer" to Nintendo could be chosen instead of the ones chosen now. I wanted Professor Layton, Phoenix Wright, Banjo & Kazooie (at least got that), Rayman (or even the Rabbids), Geno and Shantae as third party, because I feel like they have been a part of
NINTENDO history, what Smash is supposed to celebrate (to me at least). Hero did this well. Byleth was an okay choice, I'm not really into Fire Emblem, but Byleth had a nice moveset, and first and foremost: first party characters were back on the table again.
Now, Arms is announced. It got me immediately excited. Back to celebrating Nintendo history with Smash Bros. again. This gave me hope for the rest of the characters. Hopefully a more Nintendo-centered cast, and I really want some first party choices. Since Arms can destroy the rule of "spirits can't be characters", I'm back in excitement because that means more Nintendo characters can come!
However, a third party with the name of Professor Layton is still my #2 want. Because it's a big part of my childhood AND it's a big part of Nintendo's history (the huge DS era). While anything Rhythm Heaven is still my #1
(and Arms was my #3). RH looks like it's impossible for Smash Ultimate, so my biggest hopes are on the professor!