What is there to talk about Half-Life 2 that hasn't been said thousands and thousands of times? If Half-Life 1 is a fun game that revolutionized the way stories can be told in games, Half-Life 2 simply revolutionized the way games work.
It's almost unbelievable that this was released in 2004, its graphics are frankly surprising to this day, physics are perfect, gameplay is adorable, storytelling is superb (and such a great atmosphere). The only thing I could complain about this, is that I didn't like the ending, but hey, 2 more expansions to go!