First off, no reason to complain about the use of japanese lyrics for the sake of japanese lyrics. Hell, I've been studying the language for several years now, and know enough that most people are annoyed only when people over use stupid phrases they picked up watching nothing but anime. These phrases, which are not used every day like they are in anime, get heavilly overused by non speakers. Anyway, that aside, I think Japanese fits as it IS a remix of a Japanese composer's song. As for mispronunciation of Japanese words, yeah, it's common, but far less so in more serious stuff. Someone compared this to Utada Hikaru (I totally agree), and her language is much cleaner than say Gackt or Miyavi. Slurred up lyrics would just sound out of place in this song.
As for the song itself, I don't know if I can say anything bad about it. While most people I know seemed to be annoyed by the forest temple theme, it's always been one of my favorites, especially the echoy oh-eh sounds. I think you did a really nice job in replicating that effect. Nice and calming like the original. I'm looking forward to seeing more work from you, and seeing you doing vocals for some others. 'd imagine you might make a nice fit with Jeremy Robson, Nigel Simmons, or maybe even Zwitra. Keep up the good work.
*Edit*
Yeah, agreed, native american comparisons are a bit much. I'd be more likely to argue Enya does Polynesia or something
-Karrde-