I'm really loving the modes they brought back as well as the new modes for Single Player. Event mode feels fun and challenging, Master Orders and Crazy Orders feel very fun yet risky at the same time, and and Classic Mode has a different feel to it I really like. I managed to beat Master Fortress the other day, absolutely insane battle. It's so nerve-wracking because they bring back enemies from Smash Run that you should DEFINITELY FOCUS if you want to win. Especially those assholes who start glowing, as their beams are incredibly dangerous.
Smash Tour is great fun too. It feels like the old Mario Party with a lot of randomness, interesting "mini-games", and a lot of items to fuck your friends over. Nothing's funnier than starting up a Home Run Contest or Target Blast and shrinking them right before the battle. Plus you get a shit ton of loot after the battle which is a godsend. Trying to unlock more and more stuff in this game seems a lot more random as trying Classic specifically for Custom Moves seems super random.
Visuals and music are fantastic. I never knew I wanted a Smash in HD until now and damn does it look and sound good. It just works, I really like it. Lag's very minimal too. You can also add randoms to your friend's list and you can even use Custom Stages online with friends even if they don't have the stage! I love those features. Can't wait until they add downloading for stages and photos.
This one just feels like the definitive version. I liked the 3DS version and I'm glad I can play it, especially to import custom characters over while I'm trying to get more customs, but I'm definitely sticking to this one for the good stuff. Couch gameplay just feels right.