Great game, but don't expect it to be too much like the previous titles.
Gran Turismo is a really great game in most aspects, but is more for a bit of a leg-up if you have a PS3 and are getting GT5 since I heard you can port over your entire garage. I myself don't have a PS3, and although it's a pretty cool feature, I'm looking at this game based on it's own merits.
The game modes are quite good, but what deeply saddened me is although going through the Driver's Licence tests are progressive, the actual single player races are not. There is no real Career Mode. Where the previous titles always had championships and endurance races and the opponents usually had set types of cars for the race, this only has single races that you can choose the amount of laps for and the opponents cars change depending on what you drive. Also, the lack of installing new parts for your car takes away from the experience as well.
The actual racing is extremely well done, with car physics and drafting being pulled off very well. The controls are quite good as well, although steering with the analog can be a bit tricky at times. Luckily for those who are not analog-inclined, you can always use the D-Pad. I'm very glad to say that you can also customise the controls to how you see fit.
Graphics in this game are astounding, with the cars looking very nicely detailed, with reflections as well. The surrounds on some tracks can start to look a bit boring, but for the most part the textures are very nice to look at.
The sound effects for this game were nearly perfect. Sounds such as the engine roaring and skidding are really satisfying, especially when travelling at a high speed then tucking in behind the car in front of you, you can hear how the wind that was gusting around your car suddenly stop. Very nice touch.
The area of music was a little bit of a letdown. I found that the default music was a bit repetitive. Luckily the game developers clued on and introduced the option to listen to your own music while you race and also to make your own sub folder that you can fill with specific songs that you enjoy while racing.
The selection of cars is huge, with different cars being up for sale every 2 days for a cycle of 70 days, although again this can be annoying if you forget to buy a car since there is no way to advance the days except to enter a race.
Now, to be fair, I haven't actually had a go of the multiplayer since none of my friends have the PSP, so I did not take this into consideration when scoring. Internet matches would have been greatly appreciated though, especially by me.
All in all, if you are a Gran Turismo fan, I recommend that you give this game a try especially if you are getting Gran Turismo 5, but don't be expecting to see too much in common with the earlier games.