I wouldn't call her a 'great' singer either, but her versatility is pretty good. She grew up in America, so her 'Engrish' accent is minimal if not completely nonexistant. If you've heard other Japanese music where they sing a few scattered English words here and there, I think you'll recognize the thick accent. Utada sings entire songs in English without this accent.

The Kingdom Hearts songs fit better (and possibly are more coherant) in Japanese, naturally, since she writes the songs in Japanese. Then for the English versions of these Kingdom Hearts songs she has to fit English words in the same rhythms and tones as the original version, and the result is as you pointed out.

I watched a short program late last year that had her singing with 2 guys on a guitar and a piano, first she sang Greenday's Boulevard of Broken Dreams (entirely in English), then switched over to Passion (Japanese/Original version of Sanctuary).

But yeah, I like her. She's been the 'Best Thing Ever' in Japan for a while, not just because she sings for these 2 games :P She's one of the 2 top J-Pop Idols over there (the other is Ayumi Hamasaki).