A review of game is simple. It documents the players oppinion of the game, but also the Pros and Cons of each major Game aspect....Graphics, Gameplay etc etc. A review like-
This game sucks. Don't d/l it. is an abomination. It's a comment at best and even thats pushing it.

A perfect example of an uninformative and completely unhelpful review is this one of Eternal Daughter.
http://www.create-games.com/review.asp?id=729
I realise that not everyone likes ED and that is their right. Everyone bagged Podunkian for giving it a 3, but he said why he gave it a 3.
http://www.create-games.com/review.asp?id=537
That 1/10 would be great if he didn't give a reason worthy of a 3 yr old.

Also a game should not be reviewed unless you've played the game for at least-

Newbie/Beginner Game : 10-20 minutes (This is for the standard newbie game. There are occasionally some very good newbie games which may require longer)
Professional Platformer : 1hr
Professional RPG : 2hrs
Other : 30 minutes

This should give you enough time to get a feel for the game so's to give a full review not based completely on your first oppinion.

Newbies should read this article in particular. When I was a newbie my reviews were pretty poor too. But I have worked up a system.

1. I give an intro stating basically whether I like the game or not.

2. I comment on each aspect I deem nescassary.

eg: Gameplay : Very good. A little slow...bla bla
Graphics : A little plain but.....
Sounds : Bla bla

And so on. In each comment I state good points and bad points. Usually I also state some possible solutions for the bad points.

3. A conclusion that sums up your stance on the matter. Should have
*Whether it should be d/loaded
*Quick dot points of possible improvements
*And Good/Not good.

This is the recipe for an informative and useful review. Please follow this simple formula when composing future reviews.