You might be wondering why a game in the Game Library is sometimes voted (by one person) at 3 hearts, while another is at 5 hearts. It's all subjective, and the more votes received the more a "consensus" of a game's value begins to emerge.
But in case you're unsure how to vote for a game you've played before, and you want to participate, it works like this:
Horrible
Bad
Good
Very good
Exceptional