Very different. Ripper is an excellent vocalist. Everything he does on disc, he pulls off live. His work on the "Gettysburg" trilogy gives me goose bumps every time I hear it. However, to many, he's merely a Halford clone. And perhaps even more importantly, he's not Barlow. Consequently, he gets unfairly criticized.
Barlow, had a very unique voice and that voice became integral to Iced Earth's sound. He sang with more passion and feeling than anyone I've ever heard. He had range and power. He could go from heartbreaking, smooth lows to ear-shredding shrieks at the drop of a hat. Short of Tate, he's the finest Metal vocalist ever (IMNSHO).
To hear each singer at their best I'd recommend the following songs:
Barlow - Dracula (off "Horror Show")
Owens - High Water Mark (off "The Glorious Burden")
By the way, if you're new to Iced Earth, simply go buy everything from "Dark Saga" to present day and thank me later.
Zod