Let's celebrate the end of the decade by picking the best game in their respective year.
Note: I decided to only add the top 14 games according to Metacritic for the sake of not making a massive poll - unless the user score is below 70, but you're free to mark the, "other" option and say your reasoning here. Also, excluding ports or an updated version, example Super Street Fighter 4. Also, for this year sports games as 3 got above a 90 and it wouldn't be fair for games like Deus Ex.
My personal pick is Portal 2. The co-op was simply incredible, but the ending was amazing. It was in my opinion one of my top 20 games of all time.