Despite the limitations of the PSP, its still a decent racing/driving simulator.
Unfortunately, there is no career mode. Its more like a glorified arcade mode from past GT games. All tracks are available from the get go. You start out racing at the lowest difficulty and after winning, the next difficulty is available for that track, then repeat for the next track. The higher you place, the more credits you can earn to spend on more rides. There is also a Driving Challenge mode available. Its similar to the license courses from past games. Some will time you on how fast you come out of corners while others will time you for a whole lap with preselected vehicles. Depending on what time you score, you can earn credits. You also have a time trial mode which is pretty much standard for racing games. Ad-Hoc multiplayer is featured as well. You and up to three friends can race each other. A neat feature in GT is the ability to create a custom soundtrack. You can import your favorite MP3s into GT so you can listen to them during races. Most Im sure will like this feature because during a race, the same song will loop over and over rather than change music tracks like in the console GTs. Some of this music is annoying to hear over and over again so this feature is a blessing.
The Good: GT features over 800 highly detailed cars. Amazing for such a small package. Most of these cars were ported over from GT4 but it also features some newer models that will make an appearance in GT5. The tracks, with the exception of one, are also ported from GT4. The other one was ported from Tourist Trophy. Overall, a total of 35 tracks are here with some of them having the feature to drive both forwards and backwards around the track. Decent graphics, not quite on par with its PS2 counterparts but still decent for PSP. An in-car camera angle that some will enjoy but the dashboard is all black and its pretty much the same with every car. The car physics are realistic as they should be.
The Bad: Only four cars can race at a time (The console GTs allow for six). Limited tuning. Only the cars on your favorite cars list can be tuned. Only four dealerships at a time can be accessed, new ones pop up every two or so career days. Some of the race tracks could use a little more stitching, for example: On one track, you will see a line in the road. This was more of an issue with some PS1 titles. Also, some of the background such as hills or mountains are horrible to look at. Long loading times, the optional install option should remedy that but you need to set aside 750MB of space on your flash stick. No car damage.
Overall: The Gran Turismo formula demands so much and the PSP cant quite fulfill all those demands. Still, its forgivable. For a portable Gran Turismo, its decent. Fans who want a GT on the go should be satisfied, a great title to hold over fans waiting for GT5. Newcomers to the series should play GT3 or 4 first before going with this. For people who play fast and hard hitting racing games, like Need for Speed or Burnout, they will probably be disappointed because this is all simulation and not the action and arcade racing titles they are used to.