He is a rapper. 90% of his work has been rap. He 'sang' a few short hooks here and there until his 808s and Heartbreaks album came out (where Love Lockdown and Heartless are from), which was almost entirely sung. All very heavily auto-tuned, because he is NOT a singer and cannot carry a tune, but he also has an obsession with overworking his vocals until they're robotic. But, Kanye's one of the most heavily critically acclaimed hip-hop artists ever. He's a brilliant writer and producer and has a keen ear for great samples. I do so wish someone would convince him to never, ever sing again though.
(and no, no one needs to reply to this just to tell me how much they hate Kanye, this is the DIS, I know none of you are fans.)
As for the Miley performance, I wasn't shocked...I was just full of second-hand embarrassment for her. Cringe, cringe, cringe. She's trying way too hard to turn her teen pop image into some kind of street cred and it's just awkward. Two years ago the girl whined about the lyrics in "Party to the USA" saying "I don't even know who Jay Z is!" and now, after such a short while, she's giving interviews saying "I don't know who One Direction is, I only listen to URBAN!"

I look forward to her next "phase". Maybe her next obsession will be Polka music. At least she'll be fully dressed then.