It was this price a few days ago for PS3 only, now its on both platforms for the weekend sale! Next cheapest looks to be Zavvi at £34.45.
It has good reviews across the board, a great return to the roots of the series. Currently 87 & 89 on metacritic for 360 and PS3 respectively.
Also £24.85 on PC, though this isn't as good a deal, may still be the cheapest around at the moment - £24.91 at amazon, £24.99 at play.