More fun and probably more realistic than Gran Turismo 4 (which is awful, the worst of the series by some margin imo), thankfully. That's what I was expecting it to be, but taking into account the lack of a proper "career mode", the 4 cars on track max, no night time, and other little things, GTPSP is far better imo.
I know it's just a GT game and it's only on a portable gaming system with one crappy "analogue" nub and digital buttons for brake and throttle, but taking those things in to account it seriously is impressive. The car behaviour is spot on, and I get the same satisfaction from "driving" quickly in GTPSP as I have done from any other console racer where I'm using a control pad. Super smooth graphics only let down by washed out textures, but the cars look really nice and the cockpit view is also actually very good. "Squint and it looks real" replays too, with GTs unsurpassed camera angles, replays that are actually worth watching.
I rarely touch my PSP, which I only have in the first place because I bought it dirt cheap, and I certainly wouldn't sit at home playing this, but this game really surprised me, full marks.