Little Mac is actually the Only Nintendo Character in Smash I was really, Really excited to see being added in (I started the Series with Brawl for reference). Mewtwo coming back was also cool for me, But I spent the first days/week just playing Little Mac in Single player and online
So I will say that on Mac, I will say that having no air game is very limiting in what you can do, Especially in Ultimate where the Air is more centralizing then Smash 4, that and everyone is Faster, so Mac doesn't have as big of a Gap in speed in such. I also don't like they made his Down tilt more laggy
But I like how he plays, I think just make it so his Aerials are less laggy so it's easier to Chain into Specials, so his aerials would still suck on their own, but they could be useful in setting up into His Specials (Jolt Haymaker and Rising Uppercut). It gives more reason to go in the air as Mac. Mac should still be a ground Fighter mostly, but have more options in the air man
And Honestly, I love abusing it when I'm playing Mac, Especially in Single Player, but I think the Super Armor on the Smash attacks has got to Go. It's fun, but it's also Toxic and skews the Risk/Reward in terms of Contesting Mac on the Ground
I know this is probably a less popular view, but I really get a lot more joy from seeing the franchises already in Smash getting expanded Vs new ones introduced.
Like Ultimate was fantastic for that, new Metroid and DK characters for the first time since Brawl. New Xenoblade and Final Fantasy in DLC. A second animal crossing character. Star Fox and Zelda got cut characters back. We also got Ken. This on top of typical new Mario, Pokémon and Fire Emblem. The main thing Ultimate lacked was new stages
The next game, I'd like to see newcomers from Zelda and Kirby. Both of which have highly requested characters and haven't received anything new, character wise, since Brawl.
My personal opinions on this withstanding (there are still a handful of series I want to see that aren't here yet), I feel like that's largely what we're in for. Switch has been very light on the new IPs, so aside from Ring Fit there are no obvious layups from recent successes or experiments. Astral Chain exists, but I'm not totally convinced on their odds. An old school pull seems viable as always, Golden Sun has good support moving forward, but beyond that... the Switch era has been about bringing existing Nintendo series to the next level, and I feel like that's where the focus will be at.
I do think, first and foremost, this means Animal Crossing and Splatoon. Rapidly growing series that haven't gotten the opportunity to build up its major players yet. But Zelda and Kirby have bold new entries too, so I think it's definitely on the table. I'm still a bit burnt about Rhythm Heaven getting skipped again but I'm also glad that DK and Metroid finally feel whole, so I'm not mad at the direction they chose. Isabelle was a must too.
I honestly think that more than any Franchise, The one Franchise that's very untapped in Smash, and I think should honestly get more focus if they do decide to focus on Nintendo Newcomers is the Biggest Media Franchise in the World: Pokemon
Other Franchises Like Kirby, Zelda, Splatoon, and Animal Crossing have been busting numbers on the Switch, Especially Animal Crossing, But I think with how Pokemon works in that there are so many Pokemon, each with Differing Designs and abilities and many of them having a Fanbase, and with it being as big as it is, it's kind of a Crime That Pokemon have kind of been chosen as just "Shill Picks" since Smash 4.
Granted Greninja and Incinearoar turned out to be Popular Pokemon anyways, and fun picks, but I think Pokemon could have a say in having 2-5, or even more Newcomers in the Next Smash
I'm not even that big of a Pokemon fan at this point in time, but I think Pokemon would probably be the main selling point in a "Strong 1st party Newcomer lineup", especially to Casuals
Also for Astral Chain, if they were to get in, I actually kind of see them as DLC Material, rather than Base game. Being a Character Action game, The Howard Siblings would likely get some new Abilities and Legions in the 2nd game, So maybe it's better to wait to implement them until then, since I assume it's getting another game since Nintendo bought the I.P.