The format I use for reviews is: an introduction, summary of the story (not included if not a story heavy game), what I liked, what I didn't, and a conclusion. I will need at least a day to play the game depending on the length. So I can get a complete feel for the game and write the most accurate review. A review takes me between four to five hours to finish.
What the Seller needs to start the work
A copy of the game if it hasn't already been released.
Permission to post my review to my site.
And I must be able to say it's a paid for review.