Ornn's ultimate strikes me as awkward and lackluster designed. The rest of him is fine though.
The delay before the Ram first comes in towards Ornn is too long the pause where the path is lit below stirs this awkwardness which is from that combined with that strange low horn sound that gets played when the ultimate starts.
The ram should come in instantly and the sky should also get dim and slightly red almost like an effect like how
goes into ult. Catch my drift?
This gives his ultimate a real feel like there's balls behind this champion so you'll shit your pants when you see the sky change color. It gives a more dramatic effect. Change the sound too make it more sharp and impactful.
Other than that the rest of him is well thought out and he seems like a well designed champion but his ultimate like i described is off.