Here's a summary of the Nintendo Direct for those (Mop it up) who didn't want to watch the whole thing.
1. More starting characters in the Wii U version.
2. The Wii U version is in HD. Shocking, I know.
3. Up to eight-players, but only on certain stages. Not available online.
4. Bigger stages detailed. Hyrule Temple from Melee returns. There's a bigger version of Battlefield called "Big Battlefield." There are "special combat conditions" for this stage; he did not elaborate.
5. The Great Cave Offensive stage revealed. It has "Danger Zones
" that will KO you automatically if you're above 100%.
6. Jungle Hijinx stage based on Donkey Kong Country Returns revealed. It has has two planes, a foreground and a background, to fight on which you move between with Barrel Cannons. Using a Barrel Cannon will surround a fighter in flames temporarily (visual cue, causes no damage), but using it again immediately while surrounded by flames will cause the fighter to blow up. This is probably to prevent Barrel Cannon spamming.
7. Wii U version has more stages than the 3DS version. There's a reel of stages from both versions. I'm not going to list them all. Wrecking Crew is new (I think). They showed the Mario Circuit stage from Brawl and a different Mario Kart stage based on Mario Circuit from Mario Kart 8. 75 M is back for some reason though it might actually be fun this time with 8-player battles. Also, it looks like the past stages have gotten an HD touch-up. No sign of stages from Super Smash Bros. on Nintendo 64.
8. Miiverse Stage revealed, same set-up as Battlefield. Miiverse posts will show up in the background. It will not be ready when the game releases.
9. Palutena, Viridi, and Pit have short conversations about the fighters in the Palutena's Temple stage if you pick Pit and use his down-taunt, like the codec conversations in the Shadow Moses stage in Brawl. There are some cameos (e.g. Chrom). You can also listen to Star Fox team's radio chatter in the Orbital Gate Assault and Lylat Cruise stages.
10. Gaur Plains is also available in the Wii U version, but Metal Face shows up at night and makes the stage annoying. He talks a lot and can be KO'd.
11. Ridley is a stage hazard in the Pyrosphere. Attack him enough and he fights with you. If he gets killed, that counts as a KO (sounded like only for
the person who scored the KO, not against
the player whose side Ridley was on) and you can KO him even if he's fighting with you. He can also transform into Meta-Ridley if he "consumes a certain type of energy." The segment ended with Sakurai drinking an entire bottle of Caterkiller's tears; he said it was the most delicious and refreshing beverage he's ever had. I may have made that last part up.
12. Coin Battle returns.
13. Stamina Battle returns.
14. Special Smash has a bunch of different options to create crazy matches. It doesn't affect your records.
15. Item frequency option returns. No mention of the 3DS version getting updated.
16. My Music allows you to change the frequency of songs that appear on the stage. This is the same as Brawl unless I'm mistaken.
17. Menu music can be changed.
18. **** ton of music. The Wii U version has more music than the 3DS version, but we already knew this.
19. There are more composers in the Wii U version.
20. Collecting CDs nets use more music. Some can be obtained by completing Challenges. Same as Brawl.
21. There are 140 Challenges, all on one page (3DS version has 105 split into three pages). Apparently, the Challenges are harder than ever.
22. Classic Mode in the Wii U version is different than Classic Mode in the 3DS version. You do not choose paths. It's skill-based and you advance based on performance. You can adjust the intensity like the 3DS version by using coins. Classic Mode can be played with two players! Looks like you get both trophies if you complete Classic Mode with two players using different characters.
23. Clearing Classic Mode shows you a short movie of the character you use, similar to Melee.
24. Unlike All-Star Mode in the 3DS version, you fight characters in All-Star Mode in the Wii U version in reverse-chronological order. It can also be played with two-players.
25. Event Mode returns. It's no longer a list of events. The event matches branch out on a map. There are different paths though he didn't specify if they unlock under certain circumstances. There are different difficulty levels for the events which yield rewards on Hard (possibly on Easy and Medium, but the example shown was on Hard). There are some two player Events as well which has a different map than the single-player one.
26. Smash Tour revealed, a board game mode for up to four players. Use your Mii to move around the board picking up fighters, items, and power-ups. If you land on the same space as another player, all players have to face off in a random battle and the winner can take another player's fighter. At the end, you play a stock battle with all the fighters you collected. This mode is a hard to explain. There are checkpoints that make you stronger and you can use items for strategy. If you're interested, it's probably better to watch this part to get a better idea of it.
27. Target Blast in the Wii U version is similar to Target Blast in the 3DS version. Notable differences include a larger bomb in round two (harder to hit off the platform) with a larger explosion. There are also three types of stages instead of just the one in the 3DS version.
28. Stadium Mode can be played multiplayer. Take turns in Target Blast. Play simultaneously in Multi-Man Smash. Take turns with up to four players or with two players cooperatively in Home Run Contest.
29. Special Orders Mode revealed. Not sure if I'm getting this right. In Master Orders, you buy a ticket (higher difficulty, higher price, better rewards) and you advance by completing the ticket's challenge (winning a special type of match). You get one chance to complete the challenge (lose, no reward) so you can't repeat the challenge to try to get that same reward. In Crazy Orders, it costs coins or a pass just to enter (not sure how you earn passes, but the same icon was on the Events map). Then, you complete as many challenges as you can within a set time limit to earn rewards. You have to beat Crazy Hand in a match to keep the rewards. If you lose, you get nothing.
30. Master Core has a new form: Master Fortress (only available in higher difficulty). It's reminiscent of the Zelda stage of Melee's Adventure Mode, just not Zelda themed. You have to find the Master Core and destroy it. This makes more sense than the 3DS version. After defeating the Master Shadow form in the 3DS version, the actual Master Core just sits there and you hit it until you can score a KO.
31. All the controller options shown. Changing the button layout seems to allow more freedom.
32. The GameCube controller adapter allows you to use GameCube controllers to play. Who knew?!
33. Using the 3DS as a controller requires Super Smash Bros. for 3DS.
34. Custom Characters with all the equipment can be transferred from 3DS to Wii U. This also includes Mii Fighters with their costumes and equipment.
35. **** ton of trophies, most are taken from console games. There are more trophies in the Wii U version.
36. Earn Final Smash Trophies by completing All-Star Mode with each character.
37. Trophy Box for showcasing earned trophies. Looks like a different way to organize them.
38. Photo Studio detailed. You can arrange your trophies and take pictures of them. It looks pretty robust. You can arrange them in a 3D plane and change the size of the trophies, for example.
39. Trophy Rush can be played with two players. You can team up or play competitively.
40. Masterpieces return. This is similar to Brawl, but they make a point of stating that start-up is quick (I presume because this was slow in Brawl). Demos of the games are timed and some are set up with pre-installed save data, probably to skip story/exposition and get right to gameplay. You can go right to the e-shop of the demoed game from the Masterpieces menu to purchase it.
41. Amiibo detailed. Amiibo gives you a Figure Player that gains experience fighting. You can feed it extra equipment to gain experience. You can fight or team up against them or watch them fight for some reason. The Figure Player is tougher if you bring it to someone else's Wii U, and it can earn rewards.
42. Use the Wii LAN adapter if your wifi connection isn't stable (or you don't have one).
43. Notifications show up at the top of the main menu.
44. Two players can play online on the same Wii U.
45. You can host and join tournaments, as well as set up different rules and conditions for the tournament. The Tournaments feature will not be ready when the game releases. This seems to be a recurring theme.
46. Nintendo will host their own tournaments. Up to 64-players. You can watch replays, up to two minutes.
47. The GamePad can mirror the action on your TV, or you can set it up to also show the damage percentage, similar to the bottom screen of the 3DS version.
48. You can draw on photos taken in game then share them online. I'm sure this won't descend into crudely drawn penises everywhere.
49. Voice chat using the Wii U GamePad microphone... in between matches. This is done to keep the connection as strong as possible during matches.
50. Stage builder detailed. Use the stylus to draw platforms and set up pieces. There are five themes, but they're generic again. Boo/hiss
51. You can share photos, replays, Mii fighters, and custom stages, but... again and unfortunately, this feature will not be available when the game releases.
52. Bowser Jr. reveal trailer. All the "Joins the Battle" movies can be viewed from the game.
53. Register both Wii U and 3DS versions of Super Smash Bros. on Club Nintendo by January 13 to get a two-disc soundtrack, 36 tracks on each CD. Someone call Luigi Dude and tell him to post the Super Saiyin Coach.gif.
54. Mewtwo announced, no trailer. He will be available Spring 2015. Right now, it's for people who buy Super Smash Bros. on both Wii U and 3DS. I suspect he'll be paid DLC for those with only one version.