The voice can bring many emotions - the same singer can use a raw, dark voice, or a cheerful voice, or playful, or neutral, or longing, or ... This is harder to do with other instruments. Another thing, singing is about the most basic and most social way to make music. It has a psychologic advantage most other instruments don't have. Also, you cannot have lyrics without voices. Since most music seems like a duality between lyrics and instrumentals, I'd say that leaving out voice means leaving out half of the potential.
Of course, all music has its place, and I'm glad there is variety. I'm glad there's Nightwish, Tiësto, U2, Kraftwerk, Loituma, The Black Eyed Peas, Pendulum and everything in between. I'm also glad there's Paris Hilton and Usher to make fun of and to remind us how stupid people can be. If others want to enjoy it, I'm glad they can so that I can make fun of them, too.
So, there's no need to have lyrics in a song to be able to enjoy it... Nor is there a need to have guitars, or any sense of rhythm. But (personally) I'd never state that to enjoy a song, it can't have lyrics (or needs X and Y). I really cannot pinpoint any set of characteristics as being "this makes music good/bad to me".