I think the perfect game was BioShock.
It has remained my favorite game and will remain my favorite game. The idea of what Rapture stood for and how it fell is amazing. The themes and the hidden ones make you think, sure it can get boring but after beating the campaign I spent the rest of the time until BioShock 2 asking questions and making up theories about Rapture and it's citizens. Fans went to great lengths to find answers, I know the exact location of rapture based off clues in the game, it's a game that was made to make you think.
Even with the downfall of rapture due to the addictive nature of splicing and adam, I still want to go there. It's one of the greatest video game settings ever, once you play this game, you won't stop thinking about that great underwater Utopian turned dystopia in the sea.
It also has one of the greatest lines I've heard in awhile and a great plot.