I dont think its hard to write 100 characters for a review.
The problem with reviews is that there often is no way of knowing how the addon scores on specific aspects like code quality, features, support, price, etc.
There are addons that have excellent reviews because support is awesome, while code is problematic. Or vice versa. The reviews will not show this because you only need to give a general rating and a reviewer may give their rating based upon one aspect.
I do not think that resource reviews are very meaningful in their current format.
If specific aspects are rated then it will be clear where there is room for improvement and how addons compare.