Orange Box is this year's GAME OF THE YEAR, because it is several great games in one. Halo3 was nice, but it was just more of the same. BioShock was great, but not as great as Orange Box.
Orange Box is three games, Portal, Half Life 2 Episode Two and Team Fortress 2. HL2ET is just more of the same HL2-ness, that isn't anything special. TF2 is my new multiplayer game of choice (previously Natural Selection). And then there is Portal...
The internet right now is full of Portal spoilers, you ow it to yourself as a gamer to just buy the game and come back once you have completed it. It isn't just a fantastic new and original play experience, it is very intelligent comedy and I had a big smile on my face the WHOLE way through.
Portal is simple, you wakeup in a place called Aperture Science, you get a Man-sized Ad-hoc Quantum Tunnel Gun and GlaDOS guides you through some trials. History will see it as the first true action/puzzle game, but I see the same slow paced exploration gameplay that we had in the original Half Life before Half Life 2 came along and turned the franchise into northing more than a Half Life skinned WWII shooter.
Portal Does link into the Half Life universe, but it is tagged on a bit. It's like ValVe wanted to do that, so the just did with the new stuff where they could. You certainly won't find any Aperture Science references in the Original Half Life. But considering that Portal is one of those games everybody will be talking about for years and years to come, I can't blame them for doing that at all.
As a gamer there are some games that I remember with reverence because of the story, gameplay or whatever, because they did something that connected with me. And Portal does that on many levels, I don't want to go into it because, they are all spoiler-ish I think you just need to play it for yourself.
HL2ET 2/5
TF2 5/5
Portal 5/5 (It gets a five, but if Portal was the benchmark then TF2 would get a three and HL2ET wouldn't even be rated)
Additional: I just looked at a few portal reviews and I seem to be happier with it than others, this is probably because I found Portal to be such a fresh and new gameplay experience. Plus it made me laugh, a lot.