Retrospectively looking at the PSP, I think it has 4 of the greatest arcade racing games ever made.
Ridge Racer 2 is peak Ridge Racer. The drifting in this game is so satisfying, and it has the perfect track list (circuits and songs). Type 4 is more stylish and RR7 has more bells and whistles, but RR2 is by far the most enjoyable.
Outrun 2006 is undoubtedly one of the greatest arcade racers, and the PSP version is arguably the best. There are prettier and smoother versions, but the PSP version is so quick to pick up and play.
I think Wipeout Pure is peak Wipeout. Arguments could be made for Pulse or Omega Collection, but the ships just feel right to me in Pure. I also love the simple colourful aesthetic.
My most controversial pick is Burnout Dominator as peak Burnout. Many people would say Burnout 3 and name the lack of a crash mode as a critical flaw of Dominator. I say the lack of crash mode is well worth it for the return of burnout chains. The feel of drifting and chaining burnouts in this game is sublime.
The PSP came out at just the right time to make these games. It was when arcade racing games were great. It was a flagship product by one of the biggest gaming companies, that threw all the best resources at it. It was designed with portability in mind, so the games are easy to pick up, fast loading, and with clear visuals that are easy to read.
Nowadays, using emulation these games are even better with higher res, locked framerates through cheats and are playable on almost anything.