Incredible game, really like it. Good character diversity. Fun missions that are easy to win though can be aggravating trying to do the bonus requirements. Easy to get into. Free Battle Mode allows easy pick up and play, main story mode requires a bit more time. Loading times in the main story (bringing up Konoha Village) is fairly long. Good graphics reminiscent of the anime. No real replay value.
All the missions in the main storyline are fairly easy to complete, even the bonuses associated with the missions. Gameplay essentially revolves around the same few aspects, battle, field and 'mini games', though the mini games are missions in themselves and some can vary a little bit. Some missions allow you to choose who you want to play as, some require you to use a specific character, all the non-battle missions require you to use Naruto.
There are a good diversity in characters, at the very least if you are a Naruto Fan, you're bound to find someone you like. Each character is generally unique in that you won't find someone else exactly the same, but at the same time the differences won't differ all that much in terms of gameplay and combat effects. Characters have a very small amount of customisation:
You can choose which ninjutsu they wish to use in combat, you can only use one, and the ultimate ninjutsu cannot be changed.
Some characters have different costumes to use.
Some characters can begin in an awakened state.
Downloadable content is also a plus, enabling you to pick around 8 more support ONLY characters, as well as extra missions. (Note that these extra missions are not connected to the original missions, you can download these and choose not to do any of them and still unlock everything the game has to offer easily.)
I thought the graphics were very good, on HDTV it was sharp and although it isn't 'True Anime graphics' it is still close enough for an Anime-like experience. I can't say too much on sound other than the game allows you to choose between English and Japanese Voices, dialogue has English 'Subtitles'. I thought the Japanese Voices were very good, I never tried English - I didn't want to hear Naruto going "Believe it!" all the time. (I didn't like English Dubbed Naruto Anime.)
When I played through, I easily clocked over 30 hours of gameplay time, though I don't tend to mess around a lot in my games until after I finish it or whatever. Once you reach 100% completion though, it may take you 4 days (40 hours gameplay time) or more if you don't play as much, but there is little else to do after that.