I mostly agree with the OP. Something to add...
I think each game that comes out seems to have more to live up to than older games. If a game has tried something new successfully then it will get a huge metacritic score. The 2nd game that comes out employing that same successful new way of gaming will usually get a lower score because "It's been done before". Its the same in movies.
So now days developers have to be thinking about so much more than game developers 10 years ago. They have to make sure it has immersive game play, compelling story, good graphics, good game flow, good mechanics, originality in game play, ect.
In essense as time goes on the bar gets raised even higher for new game title releases. Game critics will compare games and be more and more strict on what encompasses a good game as time goes on.