I had high hopes and feel that GTPC fell short of the mark. Good sounds, probably just a notch below DRM Revival. Wonderful skins, modest models that feel like they're from the late rF1 period. In other words, good enough to go drive until... well, then I drive it and discover the physics aren't my cup of tea, aren't even close, and I end up feeling the whole mod is more of a graphics exercise than simulation.
There's an over-reliance on large back-torque in the engines to reduce mad downshifts, too much clutch-slip when upshifting (I'm using the G25 H-shifter, no autoblip, no autoclutch), and the tires don't inspire confidence. The BMW M1 & Porsche 956, so far, are the only cars that I've warmed up to. The Porsche 934 doesn't feel alive -- for a 32/68 weight distribution, there's no polar moment of inertia and you don't get the feeling of the rear end swinging out under braking and then planting when you power out of a turn. And you can't tell that the Porsche 928 is front-engined. Overall, it's obvious that Niels & Bristow have not had any influence on this project!
Back-to-back comparisons with the DRM Revival's M1 confirm that first impression about confidence with the tires and downshifting and upshifting (yeah, I know, they're different spec cars, but, IMHO not so different it isn't a valid comparison). In DRM Revival I can turn the wheel and feel whether the tires will bite or not. In DRM Revival, you can downshift without heel & toe and not instantly spin, though it will get you loose if you're too aggressive.