I'm a die hard fan of Floyd, Genesis, Tull, and several folk artists. So yeah, vocals are important.
But with metal, they don't have to be; I can appreciate musical composition and accept that the vocals take more of a back seat. However, when metal bands have good vocals/lyrics, that just makes them all the better to me. Kamelot, Kiuas, Borknagar, Evergrey, Primordial, Katatonia, etc all have lyrics that I appreciate and add to the music for me.
Then there are bands with laughable lyrics that I still love: Blind Guardian, Falconer, Iced Earth, Sabaton, Turisas (although their lyrics are actually cool sometimes, and more frequently on their new album).