A very memorable game.
The best and worst part of this game is how it judges you. It profiles you and adjusts itself to what it finds. You want to look at everything and call all the numbers but the game will take all of that into account. It's really neat to see how things in the game change depending on the little things you do differently each time you play. The look of the characters and the dialogues can be completely different from one play to the next. There are a few parts in the game where you can go through one of two doors and you can only choose one. It's definitely worth playing again to get the experience of the path not taken before.
After having played this game a couple of times on the Wii already, I was really impressed with the PSP version. You do lose a little with not having the vibration or the motion control, or being able to use the Wii remote as the flashlight/cell phone, but the game is pretty much the same. The atmosphere isn't quite as encompassing as with the Wii but the story still packs the same punch. There is no way I want to talk about the story as I think everyone should go in blind to get the best experience.
I think that Silent Hill: Shattered Memories is a fantastic game with tons of replay value and you won't lose anything playing the PSP version over the Wii version.