Criss has a serviceable voice, but he really wasn't right for Hedwig. He never disappeared into the character, but it definitely a smart casting move by the producers. It got butts in seats.
I admit, I'm completely biased. I've seen John Cameron Mitchell do it several times over the years and as it was his character to begin with, what he does with Hedwig is nothing short of incredible. Not for one second do you think you're seeing a man onstage. His banter. His accent. His ease with an audience. Really impressive.
To me, it's the best part of live theatre: Watching a performer make something incredibly tough look incredibly easy.