A very good title, with some fresh game playing ideas, that will keep you involved for long.
You begin with your selected character, alone, washed up by the waves at the shore of a tropical island. Once in control of your character, you begin only with a toilette paper and some kind of a sleeping-bag. Forget all the socializing aspects you knew from the previous games of the series. This time your priority is to find food, and create some primitive tools for gathering resources. At a later point your goal is to build a tent to shield yourself from the tropical rains. Socializing will occur much later on the game and with a very limited range of people. At the start you will satisfy your communication needs getting along with monkeys and talking to imaginary persons, made of sand.
Another feature that I found very clever is the absence of a clock in the game, because time simply doesn't matter, since you don't have to wake up to go for work, or do anything that demands to be precise in time. Of course there are no money in the game too, for apparent reasons.
The game's plot naturally reminds the "Lost" series and the "Cast Away" film with Tom Hanks, and its game play philosophy is close to that of "Age Of Empires", in the sense that you must gather a certain quantity of a resource in order to be able to build specific items. Also as it happens in the strategy games, as you progress to the story, you upgrade your tools, you find more resources, and expand your bamboo tent to a more luxurious installment.
If I must think of some faulty aspects of the game, I would say that graphics aren't so much detailed, and the characters look a little rough. I haven't played it in other platforms to be able to compare, but I believe that its appearance is bounded from the PSP computer engine limitations. Also the gathering routine, after some time tends to be tiring. But the overall gaming experience isn't much affected by these.
An issue for this game is the big loading times and the crashes that may occur. Although it appears as a big problem for the gaming experience, I don't know if it is fair to imput it to the game itsself , but rather to the UMD based mechanical and computing structure of the PSP.
As a conclusion, I found "The Sims 2 Castaway" a very interesting and addictive game, with some strokes of humour too. I recommend it to you.