I-Ninja
I got around to finishing this up yesterday. The problem I alluded to earlier (#64) is present all the way to the end: there are 21 normal stages (including area bosses) with Grade rewards before the final boss, and you need 38 Grades to open the door to the evil Emperor O-Dor. This is no Super Mario 64; getting more Grades doesn't involve new challenges as much as it involves doing the same level in a slightly different way. The monotonous backtracking really kills what would otherwise be a consistent stream of fairly creative content.
The level design is actually quite good. There is a great deal of variety in the default goals of the stages, though a couple of them toward the end are a bit on the lengthy side. The first few boss battles are very creative - usually fought in the cockpit of a giant fighting robot or other mechanical weapon - but the last ones are just ninja-jumping and sword-slashing. Ninja's combat system is solid, but not very deep (with the exception of the aforementioned occasional 'action tube' miniboss fight).
In fact, that can unfortunately be said for most of the gameplay mechanics in I-Ninja. There is a great variety of obstacles to overcome, but the vast majority of it, including fighting, is done by tilting the analog stick and/or pressing the B button. While it is fun to do, in the end it doesn't create much of a sense of achievement.
The game's plot fails to impress, as it revolves largely around juvenile humor (which, somehow, managed to produce several voice-acted cutscenes). I can't really comment on the audio, because I had it muted the majority of the time (other things were going on). Graphically, it's par for the times, nothing mind-blowing but certainly not bad. The presentation is passable, nothing more.
Overall, I would call I-Ninja a mildly entertaining diversion, but not deserving any significant attention.
Progress: Beat O-Dor