A good review is more than just a one-liner saying how much you liked (or didn't like) the game. Think about it from the perspective of someone reading the review - they want to know why you feel the way you do about the game.
Describe your own tastes. A reader who hasn't played the game yet would like to know if it's the sort of thing they'd enjoy. It helps to know if a reviewer has similar taste, so describe how the game measures up to your specific likes and dislikes.
Be specific. Readers like concrete details: things like the the difficulty level, playing time, writing style and quality, tone, how much the focus is on puzzles vs. story, and so on.
Avoid spoilers. A spoiler is information that gives away one of the game's secrets - the solution to a puzzle, a plot twist, etc. Many people who read your review won't have played the game yet - don't take away their chance to discover the game's secrets on their own.
If you can't avoid spoilers, mark them. Sometimes it's difficult to entirely avoid spoilers. If you really feel it's important to include something spoilery in your review, mark it like so:
<spoiler>This is a spoiler!</spoiler>
IFDB will hide the text within the <spoiler>...</spoiler> section until the reader clicks a button to explicitly reveal it.
Avoid referring to other member reviews on the page. The order and placement of reviews can change, and people can edit their reviews, so any references you make could lose their context and become confusing as the game's page evolves.
Be courteous. Please don't use profanity, attack other users, or stray off the topic - try to keep the focus on the game. See our Code of Conduct for more details.
Keep the length reasonable. We recommend in the neighborhood of two or three paragraphs: long enough to give a detailed review, but respectful of the reader's time. That said, it's fine to go longer, even much longer, if you have a lot to say about a game. We just don't want you to feel like you have to fill up pages for a homework assignment.