You get merits by leaving especially thorough and constructive comments as a game review. If you look through some of the games, you will see large bolded comments. These are comments that have been merited. Take a look at some of them to see what sort of comments get merits.
^^ of course by saying, "just rate games all day," you are meaning to actually play the game right? Haha, rating every game without playing is obviously against the rules.
i was going to say playing games, but that gives you no points so i just said rate games