He has a good voice, but I actually don't think he's vocally very versatile at all. I think he was totally miscast (vocally) in Piazza and South Pacific. He's more suited (if really only suited) to pop styles (I enjoyed him more in Hairspray and Finding Neverland). He's also a light pop tenor, whereas I would have hoped for a deeper, richer sound for the Grinch. Maybe he'll surprise me in a great way, but I'm not sure.
But - I'll still be watching, because I'm ultimately grateful that NBC is doing this at all.