Is it underwhelming? I don't know.
Am I underwhelmed? Yes.
Here is why.
In any kind of crossover, what's important to me is to see the characters I know and love. And at my core, I am a Nintendo fan - an old one. Before SSB64 was released in Europe, I was ungrily reading anything I could find related to it in the magazines, cause there where no Internet back then, and before I touched it, I was obsessed by it: Mario, Link, Yoshi, Kirby, Donkey Kong, Luigi in the same game?! Fighting?! It was a dream. I didn't know the other characters, but I assumed they had to be great since they were apparently on par with those icons. Pokémon was still this wierd japanese stuff we were not too sure about, except that it was seemingly huge. So the moveset is clearly secondary to me: what matters most is who the character is, what good memories does he bring back.
Now lets look at the DLC.
Piranha Plant is still, for me, the worst idea ever implemented in Smash (except maybe tripping, but I never had Brawl). That's a character I know, sure. But it would have been accurently represented by a stage hazard or a trophy - like several Mario mooks already are. Instead, we could have had... someone else. Someone from a new franchise, or an important and beloved character from a franchise poorly represented. Yes, Sakurai had very specific criteria for this "spot" (not a hero, stuff like that), but those criteria are exactly what I disagree with. So after that, I assumed the team was going to make choices that wouldn't appeal to me, and I luckily didn't buy the pass.
Joker : I had never heard about Personna, so I have no connexion to him. That doesn't mean I think it was a bad choice: that means I have no opinion on him and thus don't want to play as him.
Hero : I had heard about Dragon Quest, of course, but I have never played any of the games, so I have no connexion to him and am not willing to play as him.
Banjo & Kazooie : the only character I was delighted to see, and the only one I am planning to buy so far. Banjo-Kazooie was huge back in the N64 days, which I still see as my "console of heart".
Terry : I had heard about his serie(s), but never played it. So I have no connexion to him and am not willing to play as him.
Byleth : Come on! Another FE?! Yeah, yeah, rotating cast, blablabla. But why does every single Smash iteration must have at least one FE newcomer? Because their last game was a big deal? Yeah? Breath of the Wild was also a big deal, and all it got was one stage, and a few alterations to Link! Again, this slot could have been used for a new franchise, like Golden Sun or Rayman, or from an important and beloved character from a franchise poorly represented. The only choice of the first pass that I consider inherently bad, where the others (except for Banjo) where just "not for me".
Min-Min : Never played ARMS, so I don't care.
Steve/Alex : Never played Minecraft, but of course I know it's a very big deal.
Sephiroth : Never played FFVII (it's on my lis), so I don't care.
Pyra/Mythra : Never played Xenoblade Chronicles (it's also on my list), so I don't care.
Kazuya : Never played Tekken, so I don't care.
Maybe I'm just hard to please. But at the same time, I think characters like Isaac, Captain Toad, Skull Kid, Waluigi or Dixie Kong would totally fit and shouldn't be regarded as wierd, original choices. If we look at the third parties, it's the same with Rayman, Bomberman, Eggman or Tails. Actually, those characters not being in is what seems odd to me. Wich doesn't mean that the newcomers of the pass don't deserve to be Smashers... but I don't know. It's not for me.