Each character plays different because each one reacts completely different to different uses of the attack button and joystick. For example, on Naruto I can tilt the stick the same time I hit the attack button the first time and launch 2 shadow clones forward to start attacking. On Sasuke though that would be a lunge of a punch, which leaves him more vulnerable than Naruto, who hangs back while his clones attack in that instance. Of course, the move you use is dependant on the position of the joystick. For Kankuro his puppet does the attacking, and the way to be good is to position your puppet between you and your opponent, since they can't hurt the puppet.
They also have different shurikens, ninjutsu, and ultimates. Naruto has to hit you with a tossed clone to activate his ultimate. Shino sends out a wave of bugs all around him, making his useful to those opponents trying to get behind you. Some people's Ninjutsu are just attacks like Naruto's Rasengan. Sakura however drops a tripwire trap and Shikamaru launches 4 Kunai with explosive tags tied to them, so if they hit they damage and explode but they also stick to objects and the ground, doubling as traps.
To add more to this you can almost completely customize your character by picking their equipped items, Ninjutsu, Ultimate Jutsu, Assist characters (and the Ninjutsu they use), so the amount of varying playstyles and strategies are nearly infinite. All that said, anyone can learn the controls, and the ability to be good is in coming up with your own clever strategies, not in learning complex combos.
