These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Crowning Music of Awesome: Final Valley Version 2 from Revolution 2, found only when Naruto faces Sasuke in a one on one battle in the Final Valley stage. And yes, it returns in Revolution 3, when the two face off again. Considering by that point you're a fairly experienced player, this can make the battle a Crowning Moment of Awesome as well if the match is between skilled players.
From the first game, Akumaru, who, being a dog, is so short that everyone's attacks go over his head.
Also exclusive to the first game, Crow. While he doesn't have many great combos, he doesn't flinch when attacked, so he can freely interrupt enemies' combos.
Sasuke with the Sharingan has a special which hits instantly and from across the map, with predictable results. He also has a regular combo which allows him to teleport behind his opponent and attack instantly, giving them no time to turn around and block.
Kabuto regenerates most of any damage he takes, effectively giving him far more health than anyone in the game. His combos aren't bad, either.
From Shippuden 3, Sasori's stinger attack lets him break his opponent's guard in one shot from across the screen, his regular combos are almost as powerful, and his special attack poisons the opponent on top of its substantial damage.
Hand Seals allow characters to get a boost in attack and defense, which only happens if you are using a Wii Remote + Nunchuk controller.
Growing the Beard: While Clash of Ninja/Gekitou Ninja Taisen 1 and 2 were decent fighters, they lacked depth in terms of value and combos. It wasn't until GNT 3(which never came out of Japan) rolled around that the series was being taken more seriously, adding more than one special for each character, aerial throws, and the best known combo cancel system. Gekitou Ninja Taisen 4 is the one considered best known and played by most fans, as it had fixed all the issues from the previous games, had 40 characters to play, built more upon the combo cancel system, and added new Three-Tag matches. The GNT EX/Clash of Ninja Revolution games however, have caused a Broken Base, as well as They Changed It, Now It Sucks.
Hand seals have gained this. Introduced in GNT EX 2, players who used the Wii Remote/Nunchuk were given the chance to perform a certain motion control that can boost speed, defense, or attack power. The problem? This mechanic is not available for Gamecube or Classic Controller players. TOMY's solution in Clash of Ninja Revolution 2 is the ability to turn it off for tournament players. However, in Revolution 3, if you play a match against the AI or an online match, they still can use it against you.