5 - The Orange Box (Xbox 360)
I'm going to come straight out and say it - I don't get all the fuss over Portal. I'm not saying it's a bad game, but in my opinion it wasn't enough of a game to warrant the seemingly unanimous praise it received both from the press and gamers alike.
Yes, the boss battle was truly funny. The ending tune is definitely Grammy material. But what about all the stuff before that? Most of the time to me it felt like less of a game and more of a tech demo. I vaguely remember enjoying myself at some point during the first part of the game, then marginally maybe a bit more during the escape part. Blink, though, and you'll miss it. Just as I was starting to enjoy myself, it was game over.
For me, Episode 2 was the real meat of the Orange Box experience. That's why I bought the game. Before I got stuck in with Ep 2, I enjoyed running through both Half Life 2 and Episode 1 again, mainly for the achievements. Episode 2 really made the purchase worthwhile and that ending... just wow.
I'll admit that I have yet to try Team Fortress 2 - the one time I did fire it up the matchmaker didn't find any games for me to join. However, the rest of the package - the entire HL2 experience and that song with a game tacked on - was well worth the price of entry.