Of the list you provided I would suggest PGR2. I have no idea how many hours I've spent on the single player game
alone, not to mention Xbox Live. It's the game that keeps on giving, something you can always turn back to as it's never truly "finished". Great handling, great graphics, and none of the big grueing courses.
Well, only one - the final challenge in the world series (Nurgergring) that lasts about 15 minutes.
That said there were two other suggestions that caught my eye: Metal Arms and Beyond Good & Evil. I've played the former as a demo and it was amazing, and everyone who has reviewed has loved, possible contender for sleeper of the year. Caveat is that it is supposed to be extremely hard. For BG&A it's now a steal since the price dropped out and another on my list. Garnering consistently excellent reviews and looks to have a lot of great style and gameplay, although supposed to be a little short. Actually, because it's not too lengthy may be just the title to fill in the gap before Gaiden.