Easy and short...but fun.
I-Ninja is your typical platformer that has a great variety of gameplay built into each level. Not only is there hacking and slashing enemies galore, but there are also walls to jump, walls to run across, ropes to swing, balls to roll, and barrels to explode. Sounds dumb and like nothing unique, but they are in their own respect. Another awesome part of I-Ninja is it's boss battles. They are inventive and fun. Despite the game being terribly easy, it is a worthy of playing overall. You can get 100% complete your first time through, like myself, if you take the time. While the game is fufilling though, there isn't much replay value. I haven't touched the game in 2-3 years, however, after writing this review, I might go back and play it again :P
Graphics:
They really aren't anything polished or shiny. Just basic cartoon style. I love the character models though.
Sound:
The voices and sound effects are fitting, but the music is nothing catchy or rememberable. Nothing bad though.
Replay:
Like I said earlier, you can get 100% completion on your first time through taking your time, and then you'll probably never touch it again, except maybe the Battle Arena that you can unlock.
Overall:
I wanted this game very badly when I played the demo for it that came with Soul Calibur 2. When I got it, I was very well pleased with what I played. I definately recommend this game to anyone.