Generally you can post game reviews (for games on Armorgames) in the comments box for that game.
If you want to post a game review of a game not on Armorgames, you can do so in the gaming section (just make sure if it's flash it's in Flash).
However very soon there will be a weekly Armor Games Review Contest where you can submit reviews to a nominated game/movie/whatever we decide to possibly gain awards! Stay tuned on that one.
