I recently beat Portal on Half-Life 2: Orange Box. Although the game was quite short (about 2 hours), it was a great game. I thought that some of the puzzles were pretty challenging, and I definitely had fun trying out different ways to accomplish tasks. Portal tests your problem solving skills, as well as your common sense, and that is partly why I enjoyed it so much.
One thing that I wasn't expecting was the subtle, but mysterious storyline of the game. You wake up in a white room to the voice of a female instructor who guides you through the levels. "She" gives you plenty of helpful hints, and can be pretty funny at times. But the tide turns when you discover that **************spoilers************** you are basically just a test subject for a new weapon that the company has developed. But don't worry, there's cake at the end! The voice you hear continually mentions the fact that there will be cake and refreshments awaiting you at the end of the course. However, as you go thorough, you may discover secret rooms where, "The cake is not real!" is written several times on the walls, in blood. There is a very mysterious undertone to the game, and I really enjoyed it.
It was kind of disappointing that there was no multiplayer feature as they had mentioned before the release. I also wish that there would have been a map maker, because it would have basically provided infinite replay value. It would have been really cool to have been able to make your own puzzles and share them over Xbox Live. I guess that's for the sequel...or maybe a game expansion/update, although nothing has been said yet.
Half-Life 2: Orange Box really is one of the best values you can find. Half-Life 2, HL2: ep1, HL2: ep2, Portal, and Team Fortress 2 are all included, and are offered at the same price as any other new game. If you haven't played it yet, I suggest you go out and buy it! Even if you already have Half-Life 2, it is still worth it for the 4 other games included in the Orange Box.