I ask myself if the game's subject matter is serious, without any regard for the portrayal of said subject matter. For example, today I played a game about russian roulette, and another where you're a tornado. The first had a very 'serious' presentation, the second was rather lighthearted and cartoony, but both featured something generally considered serious so both got 5 stars. I've rarely gone below 5 stars in this category.
I'm curious to see what the 'serious' ratings will look like once the voting period ends, whether people generally considered it an ironic category or not, or if the range of perspectives on that category is so diverse that the ratings are essentially random.