I don't think it's fair to compare OS with PC directly. Yes, it's a spiritual sequel in every sense of the word. Which simply means Kamitani and Atlus wanted to have another go at the formula. But the similarities end there. The biggest similarity both games have are on purely visual and artistic levels, the gameplay has changed so much and many systems and elements have be added/changed/improved upon, etc. Come on, PC was released over ten years ago! :lol
I'll admit that yes, for some people (many people?) the game might feel repetative after finishing the first character. Backgrounds, enemies, bosses, etc are repeated as the story requires, etc. But I'll say this to Odin Sphere's credit - the game is FUN. I think what is most telling about Princess Crown's lack of replayability is that the game simply isn't that fun. It's pretty, the systems were interesting and unique, but the combat wasn't really that fun and there were many design choices that bogged the game down. Odin Sphere is fun, and unless you sit for 10 hours a day playing it, it doesn't get boring.
The game is designed to be played at a certain pace, so as long as you do a chapter or two a day, I don't think the majority of people will get sick of it. The story scenes keep your interest, the gameplay is fast and entertaining, and there's always something interesting to look forward to. Items are even more important in Odin Sphere than in Princess Crown as well, so the fact that recipes ALL carry over when you start new books makes the game much easier right from the start even if you're level 1 again. You don't feel that you're being "gimped" so the speak.