A huge improvement from the first game.
There are now 23 characters compared to 10. You start out with Naruto, Sasuke, Sakura, Kakashi, Lee, Shikamaru, Ino, Hinata, Kiba, and Gaara. This means that there are now 13 characters to unlock.
There are now more stages to fight on and more music so you won't get annoyed quickly.
The controls are still simple. They're the same as the last game (A for "Strong attack;" usually for projectiles, B for "Weak Attack"; which is used in combos, Y to throw, X to use your Special Atack, L and R to sidestep and use substitution jutsu, and a new control; Z to change targets in 3 or 4- Player multiplayer).
Now for the gameplay. The gameplay is still the same, but with more characters it's a lot more fun. Lee also has another special (Hidden Lotus). It's extremely powerful, but requires a transformation that drains his HP but gives him chakra.
If you played the first game and try this game, you will be extremely surprised because this game is a huge improvement. If for some reason you liked the first game, you should definitely get this one. Even if you didn't like the first game, you still might enjoy this game. Last, you should definitely buy this game.