RR for PSP is a gem. Absolutely still the best racer I remember playing in the last generation... music too!
Agreed. I finished the game 100% + (i.e. I did some extra racing for better times, and some of those greatly thought out timed championships), which includes the 39 World Tours and unlocking all the bonus cars and bonus movies (some people think you've finished the game when you get the first ending movie, which has some of the best sound quality ever, by the way, and beautiful graphics).
The playability was just perfect for a handheld. I loved the game to death. I never even ran into someone else who had the game, as I got the PSP 5 days after launch date in Japan, and I live in Europe, so mainstream didn't start getting the PSP until September.
I also got most of the other Ridge Racers. In comparison, the fifth that was released near launch for the PS2 wasn't all that hot, playing it in retrospect, but back then I did play it a fair bit. The 4th version wasn't bad either, on the old PS1.
If the game is anything like it's PSP cousin, and especially if it has good online modes, then I'm sure the game will do well. The 360 version got much better reviews than you think - you have to read them to know what I mean - but the 360 got PGR3, which obviously exclipsed the title, and rightly so.
In general though the RR series make for pretty good launch games, traditionally.