Yeah I got the game sometime last December so I've known it's awesome for a while now.

My friends won't play SSBM (stuck bitching over changes from SSB) so this is our main 4 player fighter.
As a fan of the anime and manga, things are looking good for future installments of the GNT series gameplay wise. The game keeps up to date with the anime, which right now is at a critical point in the story. Since GNT3 there's been about 5 or so new characters introduced (Orochimaru's 5 sound ninja, plus filler story characters if you wanna count them), plus a couple they left out (Kabuto, Shizune, maybe Kisame too), and a few character changes (Gaara's new sand attacks, drunken fighter Lee, Chouji's power pills, Neji's 128 point strike, Kiba's new merged dog attack, Sauske's cursed seal level 2 mode). Not a whole lot, but probably more than what was changed from GNT2 to 3.
However, the real money would be on what comes after that. At the pace the anime is going at, next year there should be plenty of (future anime/manga spoilers)
3 year time skip material to work with. A host of new characters, all new character models for existing ones, new moves, the works. I don't know how long the development cycle would be, but if they start now by creating models based off the manga and then waiting on the anime for animation and voicework, they could feasibly pull off GNT5 (or 4, should they choose to skip this year, but I doubt that will happen) as a launch title for Rev in Japan (or GC game at Rev launch time, since it is backwards compatible), with a possible US release when the anime catches up here in the states.
But back to the point: Naruto 3 is awesome.