Since I'm short on time (and there's so much material, and you can literally find this same list everywhere), this is merely a list with some thoughts from myself.
1. 3DS Secret Characters as starters
: Honestly a little disappointed with this. I'm all for having a different starting roster from the 3DS version, but I love
unlocking characters, and now there will be far less of that.
2. Higher resolution
3. Eight Player Smash
: HECK YEAH! I just wish I had a way to get eight people in the same room... and room for eight people.
4. Bigger Stages
: This means that the Hyrule Temple stage from Melee
is back again, and that is awesome. I love that stage.
5. Danger Zones
: I feel like they might make certain stages more annoying to play on than they should be, especially regarding the insta-KO if you're above 100%.
6. Two Plane Battles
: It's odd to see a feature like this on the Wii U but not the 3DS, but also understandable. This stage looks like a lot of fun.
7. More Stages
: This is good... I feel like the 3DS was low on stages. Maybe just low on ones that I really like.
8. Miiverse Stage
: Looks okay, I guess.
9. Palutena Commentary
10. Metal Face appears
: This is just an insult to those who want Ridley to be playable, it really is. Make him 1/3 the size he is right now and a little fast and BOOM. I mean obviously more work than that, but come on...
12. Coin Battles
14. Special Smash returns
15. Item Frequency
: A feature that should have been in the 3DS version as well.
16. My Music
: One of my favourite features.
17. Menu Music
18. Wii U has more music than 3DS
19. More Composers
20. Collect CDs in-game
21. More Challenges than 3DS Version
: Awesome. [/sarcasm]
22. Classic Mode
: My interest is piqued. The 3DS classic mode is my favourite yet, so we'll see how the Wii U version stacks up.
23. Classic Mode movies
: Haven't these been in place in the series forever?
24. All-Star Mode
: Meh, not really an exciting change.
25. Event Mode
: Looks like a refreshing change.
26. Smash Tour
: Looks very interesting! I'll definitely have to give it a few spins.
27. Target Blast
28. Multiplayer Stadium
29. Special Orders
: I feel like I won't bother with this mode much.
30. Master Fortress
: Seems interesting. If the stage is the entire boss fight (and you don't have to battle the other Master Core forms as well), I'm all in.
31. Lots of Controllers
32. GCN Controllers
: Old hat.
33. 3DS as Controller
: Also old hat.
34. Custom Characters from 3DS to Wii U
: Even older hat.
35. More Trophies
36. Final Smash Trophies
: I've made it a goal to complete Classic Mode on the 3DS once with every character. I shall make it my goal to complete All-STar mode once with every character on the Wii U.
37. Trophy Box
38. Photo Studio
: Looks like something I'll enjoy.
39. Trophy Rush
: This... isn't new. It was in Brawl
41. Level up Amiibo
: If they can become stronger than CPUs then heck yeah! And even still, heck yeah! Amiibo!
42. Wii LAN Adapter
44. Local Co-Op Online
: I'll give this a try.
45. Eventually Host Tournaments
: BZPower Tourney, anyone?
46. Nintendo Tournaments
: I wonder how many?
47. Typical GamePad usage
48. Draw on screenshots, share online
: I'll share my best pictures.
49. Voice Chat
50. Stage Builder
: Also should have been on 3DS. Looks much better than in Brawl
though, very excited.
51. Eventually share stages
: Please come soon.
52. Movies In-Game
53. Club Nintendo CDs
: Old hat; I've known about the promotion forever and I can't wait to become eligible.
54. Mewtwo DLC
: Already touched upon, but am excited.
55. Bowser Jr. Announced
: Also already touched on.