I only own the 3DS version, but even then, seeing all the content in the Wii U verison, I have a few thoughts on this.
Mario Series: Great amount of reps honestly
; plently of stages across so many games (NSMB, 3D Land, Galaxy, Sunshine, Luigi's Mansion, Paper Mario, SMB), great roster of characters (Boswer Jr. and the Kopalings are fantastic newcomers and round out the Mario crew perfectly
) and the new Mario items are fun to use.
Zelda Series: I really wish we got a newcomer from Twilight Princess, Majora's Mask or Skyward Sword (which is ironic, considering each of those games I mentioned got an assist trophy instead of becoming fleshed out fighters) and the new stages were quite underwhelming (the Wii U version should of gotten an updated Pirate Ship HD stage alongside a MM stage :l....).
Wario: ......No Wario Land references or anything at all alongside few new stages are a bit underwhelming
.
Kid Icarus: Makes sense this IP got a lot of new content in Smash Bros. 4 (a new fighter, a clone character, a new stage per system, lots of items), as Uprising is a great game
.
Mother/Earthbound: Wish Lucas wasn't cut and that the Wii U version got the 3DS stage :l.
Donkey Kong Country: This is just sad X(. Its great the Wii U got a DKCR stage but the music selection is just.....so odd (being filled with 5-8 remixes of the Jungle theme :l), considering the series is overflowing with amazing music to remix and reuse. I would argue that Brawl did a better job representing the DKC series then Smash 4 (Diddy Kong was newcomer, the Jungle Beat stage got great remixes of DKC music from both Nintendo and Rare themselves, and the Subspace got a few levels inspired by DKC).
Pikmin: Another character (Alph being a clone with Rock Pikmin and heaver properties would have been better then just a skin honestly) and another stage (maybe one themed around Pikmin 2) would have been nice
.
Star Fox: While it really sucks Wolf got cut.....the new stage in the Wii U version looks fantastic and the new remixes are really good
. Maybe the 3DS version should of gotten a staged themed around 643D but otherwise, I thought they did a well enough job with this IP in Smash
F-Zero: It sucks that the only new stage between the two games is in the 3DS version (while the Wii U gets a HD make over of the Brawl F-Zero stage)....
Kirby: Really expected a stage based on Epic Yarn, Canvas Curse, Triple Deluxe and/or Return to Dream Land....but the new stages in both the Wii U and 3DS versions are nice
.
Metroid: No new stages based on Prime, Zero Mission or Fusion (would have thought a 2D stage themed around Metroid 2 would be cool ala the Dreamland stage in the 3DS version) and the Wii U version pushing Other M as the 'main' influence soured things a bit, but the improvements for both Samus and Zero Suit are make them fun to play as and Mother Brain alongside Dark Samus being assist trophies were awesome
.
Mega Man and Pac-Man: Just.....they nailed it man :'). Amazing remixes, fun stages across both versions, and the characters themselves are so fun to play as
.
Sonic: No remixes, no playable Tails or Eggman (....would be perfect for Smash, even as just an Assist Trophy with the classic wrecking ball), only one new stage across the two versions and no Sonic themed power ups (I mean.....why are their now Wisps as items?).......It really feels like Sonic is in Smash due to two things (him being in Brawl and being forced to include him as if they cut him, fans would have been really mad).