Neal has one of the most exceedingly pleasant, inoffensive singing voices I have ever heard. It helps that he's able to stack genuine emotion on top of it.
At first, I didn't notice his voice much. Now it's one of my favorites in prog. It's rare for someone in the genre to have an overtly "friendly" voice, but Neal really does, and it perfectly matches any project he's ever undertaken (especially Spock's Beard). It also makes those moments when he goes absolutely crazy ("The Light," "Lay Down Your Life," the entirety of "Sola Scriptura") really stand out.