All of the categories are subjective, some more than others, but try to be as consistent as you can with your own scoring.
Try as hard as possible to avoid vague statements in reviews. Make sure that your review answers more questions than it raises. It is essential that you try to always include an example from the scenario to back up any points that you make. If you are pointing out something to the designer that you feel could be improved, try to provide some ideas that the author could build on. Do as much as you can to help the designer improve his work.
Avoid giving away too much about winning strategies you used or surprises that the mission holds as you don’t want to spoil the fun for future players.
All scenarios have good aspects and bad aspects. Try to always say at least one good thing about any scenario you review and never insult a designer. They might not be as good a designer as you but even if you are handing out a score of 1.0, you still should never insult the designer. Be honest about the scenario but make every effort to encourage the designer to do better next time.
The review should contain a short explanation of why you scored each category the way you did. This does not need to be lengthy, sometimes a short sentence is enough but other times, a paragraph for each category is needed.
Taking the time to go through your work and spell checking it before submitting your review is essential. Nobody would like to see someone criticise a person's work for poor spelling when the reviewer's is no better.
First, the different scores you can give to each category:
5.0 - OUTSTANDING
Give this score only if there's something stunning and breathtaking in the scenario. This score should only be given to scenarios that are almost perfect, so be very careful when giving this score. For example you read the storyline and wish it was a book, you see the map and can imagine wanting to stroll along that little river. Scenarios with 5.0 average scores are rare and creators of these scenarios are masters of Scenario Design. Consider the 5.0 score as something you would give rarely.
4.0 - EXCELLENT
If you think the category you're rating is definitely better than average, but hasn't reached the near perfection expected from a 5, give this score.
3.0 - AVERAGE
A good scenario, no glaring problems, but there are still plenty of things that can be improved in that category.
2.0 - BELOW AVERAGE
Is mediocre or has errors or many points that need improving, but the scenario can be played and completed.
1.0 - WELL BELOW AVERAGE
The lowest score you can give. For example, if there's nothing in the story box, or a bug means the game can't be played then for that category it's a 1.0.