I LOVE the crossover celtic style of the music, especially the parts with the pipe. I'm not a huge fan of only screaming styles, though he was not too hard to understand compared to a lot of groups, I prefer the more melodic vocals like KSE or Nightwish. The screaming would probably rank it like a 5-6 for me for most songs, but the Celtic easily pops this up to an 8/10 for me.
For something fairly different:
http://www.youtube.com/watch?v=aHjpOzsQ9YIHopefully this wasn't posted already, I admittedly didn't have time to read through all 75 pages of youtube links... trouble of coming in late I guess.