Age has done this classic little harm.
Sound: Overall, I liked it in this iteration a lot more than in Brawl. The sound effects that play upon hitting an opponent are so much more well-pronounced, and the extra cacophony added to an already chaotic game makes it just awesome. The voice acting is done well all around, especially with Captain Falcon. HYES!
Music: Well-done also. The sounds range from Orchestral (starfox) to rock (mute city/big blue) to downright eerie (kraid's stage). Very pleasing to listen to, although the DK Rap could have used some work. I'm just sayin'.
Gameplay: Unique & awesome. Instead of a standard health bar that decreases towards a KO, you get a damage percentage that determines how far you fly when hit by an attack. This means characters will be flying across the screen like crazy, and this adds an extra challenge of getting back onto the stage to the fast-paced fighting. The controls are very responsive and very simple. A=attack, which can be modified with the use of the control stick, and the same goes for B, which is the special move. This makes for a crazy fun game that anyone can pick up and play, but is difficult to master.
Overall: if you can find it, buy it!