I love this song, really. I have no problem with her voice, I think it fits perfectly with the music. About the guitar part, I need this song in HQ before I judge it.
The only thing that I don't like is, the recent CD Rip version which likely will become the original mix of progress, has a different arrangement with the one in Tales of Xillia trailer, though it's a really really small part. Not sure if anyone realized about this.