Even though you don't see them much, duets in metal tend to be just regular than awesome. Maybe is the styles of the bands that one of the vocalists comes from. I've liked some, to name a few; Kamelot's Khan and Epica's Simons in the songs "The Haunting" in Black Halo and "Trois Verges" in Consign to Oblivion just fit 'cause of their styles. I didn't expect to like Machine Head's Robert Flynn and Killswitch Engage's Howard Jones combination in the Roadrunner United album. The ones that I didn't like were Hansi Kurch wih Angra(I kinda expected more from them), Meshuggah's vocalist with Mushroomhead(He completely overshadows the whole band even though i like them) and Jamey Jasta with Napalm Death(which the band overshadowed him). If you like to see one, which would it be?