I personally like a few artists with big voices...such as Aretha Franklin, Beyonce, Nina Simone. But generally it's not so important. The lyrics, emotion and honesty behind a song is more important.
Hence me not liking most musicians who're labelled as some magic, revolutionary brilliance when most of said brilliance is produced by machines. Lady GaGa, this means you.
So big voice - not important. Honest, non-edited voice = important.