-Laurence Luckinbill's performance
If he'd been playing a human character, I might agree. As it was, Sybok was very poorly realized. An "emotional Vulcan" could have been portrayed as somebody who was Vulcan first, and emtional second. As it was, he came off more as a rather gregarious human who just happened to have pointy ears. There was nothing Vulcan about him beyond the superficial.
He even contradicted what we were always told about Vulcans--that they learned to suppress their emotions because they were such a violent people. An emotional Vulcan should be more of a scary bastard.