The only justification I need is to actually BUY a game. $60 is a lot of groceries.
Otherwise you shouldn't need any. Each game has its own merits, allowing us to discover where the game excels and where it fails. And from this we can craft a better media. Or would be able, if the industry wasn't so corrupted by corporate pandering.
Of course, this is largely due to my analytical stance. Every game has something to teach us about the art.