Let's see...
1] That depends on your sim racing history (if any). Those who are already masters at the GT series, F1-2002 [PC], and the like, will get comfortable with GPL fairly quickly. Still, it can take these people a month or more to start turning competitive times. Those who only have experience with arcadey games like the NFS series, especially using a control pad, will find the realism in GPL hard to adjust to.
2] There are 250+ tracks available to download for this game. Scary huh?

The game can only handle 64 tracks in its season.ini file at any given times, so there are track manager programs out there to do the dirty work for you in creating new season.ini files. As far as cars, you can download updates to the existing 7 cars that are leagues better than the originals, in terms of graphics and sounds.
3] If you go to
www.papy.com you'll find some patches for this game. Everyone needs the 1.2 patch, those with fast processors (1.2+ GHz I believe) will need the CPU Speedfix patch, you'll need to download a Direct3D renderer patch/addition (the game could only do software rendering, 3Dfx, and Rendition out of the box), if you plan to race online you'll need the disconnect fix patch.
It's kindof a finicky game to get set-up right sometimes (I just helped a friend install the game and get all the patches last night on his brand new 1.8GHz machine, and every time we try to get in the car it crashes to the desktop... seems to indicate a display driver conflict to me but I don't know where to begin). Once you get it working right, though, it's worth it.