I don't know if Odin Sphere was one of the greatest games I've ever played...I think the actual gameplay got slightly stale after a while. The end, though, was magnificent, truly magnificent. And jeebus, was it aesthetically beautiful.
Being an English major, I actually was a little annoyed by the attempt at archaic speech... 'twas and 'twere appeared all the time, almost ad nauseum, but few other idiosyncrasies of older speech. It was a small annoyance though. Overall, I am very glad I bought it and I greatly enjoyed it.
As for Grim Grimoire...I'm fascinated, but my Wall of Shame (games I have bought but haven't yet played) is quite large, and I just can't justify any other purchases (excepting Aquaria).