Judging if you will like a game or not has to be based on two things I think:
Firstly your own experience with games. Which do you like?
Secondly, you have to judge whether or not the game fits with what you know you enjoy playing.

I find the videos on IGN particularly helpfull. Seeing the game in action, rather than screenshots, gives me a full enough picture to make a decision.

But it gets tricky when someone without gaming experience is trying to find a suitable game. I always take as much time as I can to advise someone who is new to gaming. Because if they just go out and buy a high-scoring game, expecting it to be great and glorious, they might be put off by what they get.

Grades don’t reflect whether or not the game is suitable for you, they (are supposed to) reflect how good of a game it is in it’s genre.