Even though instrumentals are rockin' awesome (post on that to follow, maybe) most music that people love has lyrics and vocal performance of some kind. We love to hear someone articulate feelings and thoughts in words, and it helps if that artist has a beautiful or distinctive voice.
When I was in 7th grade, I was completely and totally obsessed with Clay Aiken (this was when he was a contestant on American Idol). I filled notebooks with pictures of him, I wrote poems about him, I cried myself to sleep when he lost the show. Yes, I was a Claymate. Looking back now, I can't really see the appeal... I'm no longer attracted to squeaky clean uber-Christians... but I still think his voice is fkn gorgeous. See for yourself!
I can't make a post about voice without mentioning Sam Cooke. Cooke was an R&B singer in the early days of rock-n-roll, and he had tons of hits between 1957 and 1964. You've probably heard his songs "Cupid", "Chain Gang" or "Twistin' the Night Away" if you've ever listened to an oldies station for any extended period of time (or if you're like me, your entire childhood). This guy just floors me every time I listen to one of his songs. His voice is pure and soothing and beautiful. Unfortunately Cooke was murdered at age 33, when someone shot him at a hotel after mistaking him for a robber.
This song was released posthumously and is one of the best protest songs of all time. Listen to that sweet honey voice.
Then there's Bob Dylan, of course. Dylan is special because he has a TERRIBLE singing voice. He can hardly carry a tune. His voice is croaky, it's ugly, it's nasal, and it's one of the most distinctive voices in musical history. There is no way you can hear a Dylan song and ask someone, "Who is this?" Really the only acceptable thing to do is do your best impression along with the song. "How does it FEEEL?"
It's important for an artist to have a distinctive voice, even if it's not as obvious as Bob Dylan's. That's how you get recognition and fans. You have to sound like yourself, and preferably not like lots of other people. But there are different vocal styles that people fall into...
The Indie Girl Murmur
Sounds like Feist, Regina Spektor, Sherree Chamberlain, Penny Hill, Colbie Caillat...you get the picture.
The Tragic Male Introvert
Sounds like Why?, Animal Collective, Cursive, Bright Eyes
The Pop Crooner
Sounds like Bruno Mars, Drake, Jason DeRulo, etc.
You get the picture. Voice is important. Voice is awesome. Listen to music.