Well.. there are also other topics for merits that you could refer to. Well i have made 3-4 comments worth a merit but nothing yet and this is not suprising at all since moderators etc can't see every singe game in the same time! So you have to be patient if you wanna a merit.
As you said anyway a merit is a discriptive paragraph but this is true is some parts. Υou don't have to waffle just to have as more words as possible to your paragraph. You have to make a good comment in order to help other players learn something about the game so when someone sees it he would be able to understand something about the game!
In order to get a merit you must write a creative paragraph. Include alot of detail such as what you liked, disliked, ideas, proper English, grammar, spelling, punctuation etc. Just so you know it may take one day, week(s), month(s, even years. The reason for the waiting period is the moderators can not see every comment on every game at once. Just remember to be kind and helpful, and most importantly follow the rules. Have a nice day, Ethan