If you want to read a novel who some people seem to say is addicting, than get KOTOR. I personally was happy with one hour of playing and never picking it up ever again...
It has as much reading as Xenosaga has cutscenes, I thought it was pretty bad, and I don't get why nobody mentions this in reviews...
Ninja Gaiden is pretty good, but the music is TERRIBLE, and to me almost ruins the game, I'd say get Shenmue 2, you can find it for 10-20 dollars and to me it's by far the best XBox game out there, it does move rather slowly, but the story is engulfing and doesn't require reading everything, people actually TELL you the things you need to hear, you don't have to read 7 pages of text every five seconds...
Armed and Dangerous and Toe Jam and Earl 3 are very fun games as well, and if you haven't gotten Beyond Good and Evil for another system, XBox is the way to go on that one, and it's a terrific game...
But if you absolutely MUST have those two games, I'd go with Ninja Gaiden, but you do mention the price difference, and if you think KOTOR is worth picking up then go for it, I just think it's VERY overrated...
As are most XBox games...
The system is great and any multiplatform games that are released for XBox like the Suffering and Max Payne 2 always seem to be a LOT better...
But personally I haven't gotten excited over an exclusive since I've heard about Fable a year and a half ago, and now that's starting to look pretty whack too, but I hope I'm wrong...
-Goatman