Roy Khan's performance in that song was great. Really good across the scale. I thought it sounded kind of odd in some sections, but when I listened to it again, it sounded pretty good.
If only these voices were set to some more elaborate instrumentals in a grand musical composition rather than a solo or "pop singer" setting. Those live performance videos aren't really my taste, but the thread's about beautiful singing voices.
I find myself liking songs with more of a rock/metal sound. I've found my tastes transitioning to something more symphonic sounding, from Incubus, Garbage, Linkin Park, Evanescence, Flyleaf and Fireflight, Scar Symmetry, etc. to Nightwish, Lacuna Coil, Leaves Eyes, Epica... that video of Within Temptation is practically dead on to what my tastes prefer. It's very nice to see the art of music taken that far. +props to ZGoten for showing me that.
Here's one song, Ai no Zuellni, that I like that's sung by many different singers. I like the version with the original male voice (not "Layton's") and "Mayshen's" voice. It's not one of my favorites, but it's very touching and I really like the general composition of the song. I'd like to hear it sung by some of the others here.
Edit: Really? A version by Felli Loss (Nakahara Mai)? I can't find it. She has a nice soft and young voice, but I don't think she's a good match to some of the more energetic upbeat parts (Mayshen doesn't do too well either). If it was done by someone in Kokia's league...