It's a bit awkward. It's a bit off-key. And Jon's trying to sing the acoustic version, which isn't what the band is playing. I don't think it was as bad as some people are making out, but it didn't really do Jon any favours either.
Many of us fans know Jon's voice isn't what it used to be, and he needs a fair bit of warming up before he can sing anywhere near his current best, which he didn't get. The Associated Press reports that Lourdes asked Jon beforehand if he wanted to sing and he declined, so she has been copping some abuse online from fans for peer pressuring him into it.
Perhaps she shouldn't have done that song, knowing it would make Jon the centre of attention, especially if he'd already knocked back the offer to sing. But cyberbullying her is wrong.
Meanwhile, our old mate Richie Sambora -- and his partner Orianthi -- also sang Livin' on a Prayer at a recent wedding.
Check out the footage at TMZ.
IMO Richie's performance is a lot better, but since he was handed a guitar as well, he could sing in the key he was used to. Like Jon, he's doing the acoustic version, which is easier on the vocals. And IIRC, when Richie performs Livin' on a Prayer with his full band, he doesn't go up for the key change.
I say this not to criticise, but to point out that both Jon and Richie know their signature song is too damn high for them. (Hell, it's too high for me, and I'm a woman.)