Maya Grill was one of our favorite restuarants at WDW, until a bad experience in Feb 2003. Historically, the restaurant had served a southwestern/central american food oriented menu (not typical "Mexican" fare) which was interesting and very good. When we went back in Feb 2003, the menu had changed to more standard fare (non-ethnic; ribs, chicken, steaks, etc.) and was not good (food was not interesting and quality was bad). However, we were told at that time that the menu was changing back to the original format, so that is a plus sign.
All that being said, the restaurant has great maragaritas (which they serve in individualized silver cocktail shakers, which are cool) and the old/new menu (if they have changed back) was great.
The place never got very crowded when we went (on several trips, I don't think I ever saw it more than half full). As a result, it was a relatively quiet place and the service was quite good.
We skipped it for our Feb 2004 trip, but if the menu has changed back to the original format, I would definitely recommend Maya Grill.