I think it sounded like Steven Tyler on a good day. Idunno what people are complaining about. The guy is a rock star, not a classically trained vocalist. If you want Carrie Underwood, get Carrie Underwood. If you want Steven Tyler, the best you're ever gonna get is exactly what he did.
Honestly, when I read the criticism, I cringed, expecting to hear him singing flat, missing notes, adjusting the melody to fit his aging vocal chords. Instead, when I listened to the song, I was surprised that he sang the melody more or less how it goes - as opposed to all those classically trained vocalists who basically rewrite the song to showboat their talent. He didn't sing flat, didn't miss notes. The only thing he did to part with the traditional rendition was the signature Aerosmith high scream at one point. It just sounded like Tyler.