This leaked track (leaked by Britney's people to build advance hype, no doubt) has been kicking around the internet for about a week now, and most opinions range between "better than expected" and "fairly impressed". I have no idea where one draws that reaction from a track so horrible. From the opening seconds, straight from the "it's Britney, bitch" opening line (oh, she's sounding it off now, she's so baaad ... don't call it a comeback!) and the muffled, "vocals from a megaphone" whining that kicks off 90% of her repertoire, it's clear that Britney hasn't woken up to the fact that it's 2007 and she might want to try something a bit different. The beat is lifeless and pedestrian, and the croaky two-word chorus is about as catchy and addictive as piss-flavoured cigarettes. One minute and a half into it, the load is blown and the song runs out of anything interesting to say or do, and the rest is little more than endless repetitions on the chorus ("Hey Jude" it isn't), filling time until the allotted four minute time slot runs out.
postscript: I wrote this on the afternoon of (i.e. before!) the MTV Video Awards ... honest!