Not worth the money as stand-alone product. It's simply too short, period. If you have money to burn, definitely try it!
Yes, you hear that right, although the sum of all parts of the Orange Box still makes it worth-while spending your money on, basically none of the games are excellent.
I've already reviewed the Orange Box (7.5/10) and I felt it was so much hyped beyond what it really offers and Portal clearly was one of most hyped games it contained. The Orange Box still offers relatively good games, but nothing worthy of 9/10 or 10/10 scores at all. Not even for the entire package.
Qt: "When Portal was originally released as part of The Orange Box in October of last year, its uniquely puzzling gameplay and dark, sharp-witted humor thrilled consumers and critics alike"
True, the game Portal has a lot to offer and it's definitely the best game the Orange Box had to offer. However if you really feel like buying this game, go for the Orange Box instead. It's a better deal price/value-wise.
The game itself is innovative and unlike anything you've experienced and because of that alone it's a great game. The humor is brilliant, the style is perfect, the puzzles are okey. Some puzzles seem to be easier than others, especially the last part of the game is too easy in comparison to some of the previous levels, but I guess by the time you reach the latter levels Portal also 'ran dry' when it comes to new puzzle ideas. Despite that I liked the last few levels a lot more than say the first 10. It's difficult to really look at this as real critique though, as the first few levels clearly are meant to teach you how to solve puzzles, but in my opinion they should and easily could have added a lot more puzzles towards the end. There really is only a single puzzle in Portal that really made me have to think outside of the box. I would have loved to see some more of those near the end of Portal, but there weren't any. I'm not saying the game was too easy, as solving puzzles is mostly a matter of understanding the concept behind the portals and doing quite unthinkable things, sometimes solving puzzles by trial and error and messing around.
Sound and music is okey. The voice-overs are very cool, in their own way they come extremely close to the one-liners Duke Nukem used to spray whilst doing his thing, in terms of coolness. It has so much style, you'd miss out on something if you would have never played this game.
There's not much music and some sounds seem to be pretty much ripped directly from Half-life 2, but nothing to annoying going on there either.
Right, so now down to why it isn't worth the money as stand-alone game. First and foremost this is because the Orange Box is less expensive. Portal costs $19.99 and the Orange Box costs (or at least did last time I checked) about $45. Obviously you get more games in the Orange Box than Portal alone and the 'added' value it gives you is worth spending a bit more money in comparison to buying Portal alone.
This may sound complicated, but basically it boils down to Portal being a great game, but priced far too expensive as stand-alone product. This wouldn't be such a big issue for me if it was a game that lasted a little bit longer, but it doesn't. In fact, it's easily the shortest game I've played since Max Payne 2. And to make things even worse, it easily beats Max Payne 2 both in shortness and greatness, making it a difficult thing to forgive.
In all honesty there's not really a reason for not being critical about the small amount of levels Portal has and how short the gameplay duration will be. There's no multiplayer to set things right and most puzzles hardly have any replay value.
It's a bit sad really, because I feel this game really is excellent, but never reached it's full potential. It's so terribly short that it's ruining the hype for me. Did I want more of it so badly? Actually, no it didn't, I haven't touched Portal in months after I had finished it completely, only to launch it one more time a couple of days ago. I probably would not even have started the game this one more time if it weren't for a certain argument with someone about some of the hidden texts. (Which was a touch of brilliancy by the way, as it made sure the game had this 'conspiracy' feeling all over it.)
I guess you'll understand by now that there's no real replay value.
In conclusion, if you are willing to spend a lot of money for about 4 to 5 hours of gameplay maximum... that will amaze you and be like a short short roller coaster ride. Go ahead. Still, if you really feel like spending any money, you'd be better of buying the Orange Box instead.