GTR rocks people!!! Not only are you NOT restricted to having full grids, but you can race with classes. As in, if you want a grid of 20 Lotus Elises, or Ferrari 360s, you can! But, truth be told, with one Lotus in the game, 20 duplicates would be kinda dull.
HOWEVER PEOPLE!!!!
Car skinner dream come true. You can create AS many new teams as you want, (obviously making sure that their number, which the game recognises, is unique) but failing that, want to race with Ferrari 360s, and want to re-create the 360 Challenge season, then bish bash, and it can be done. New tracks can be added too. Just creating new folders and away you go. I'm currently trying to work on new tyres for teams, but trust me, if you like making up cars, and want to create your own miniture season you can really easily do it.
I think GTR is fantastic, and for the moment, GP4 has taken a back seat.