I'm really bummed about Ice Climbers being cut. That one hurts the most.
Snake, Lucas, Ivysaur, Wolf, and Squirtle not making the cut is also harsh, but not as bad as a Melee veteran being cut.
Dr Mario gets to return after not being in Brawl, but no Mewtwo. I don't think anyone ever liked Pichu, so no loss there, and Roy and Young Link have been essentially replaced by Ike and Toon Link.
But still, this has got to be the best roster ever.
Sonic, Pac-Man, and Mega Man in a game together with all of Nintendo's mascots? Yes please.
Duck Hunt Dog, Little Mac, Shulk, and the Villager are all really good first party additions.
I love the alternate costumes, too.
All seven Koopalings are in the game as alts for Bowser Jr, and Alph is in as an alt for Olimar. And though not officially labeled as such, Peach is an alt for Daisy and both Links have some recognizable costumes (adult Link has Fierce Deity and Dark Link, Toon Link has the costumes from LOZ NES and LTTP).