The critics from the Youtube's viewers -
"in my opinion, this is better than Beyonce's cover, and the actual song..."
"if she can sing this live theres no reason for her to lip sync her own songss cuz there 10 times easier to sing! ohhh britneyy hahah gaahh i loveee u tho ;)"
"she got some respect from me after this. she can sing"
p/s : For me, she's got quite a good voice. Yes, maybe not the best out there (if you guys compared to Mariah Carey) but hey, with the voice she sold over 100 million albums worldwide !!♥