Not sure if they were mentioned before on earlier pages, but I am a bit curious. What was wrong with certain vanilla cars that they ended up being replaced, by somewhat worse versions? First example being the Aston Martin DB9, replaced with a DBS. I never really noticed anything bad about the former, but the latter one has weird shadows that also several other add-on cars have (only the outlines of the car make a shadow, not the entire car, unless you're underneath a shadow cast by the enviroment), which I've also noticed on a certain Ford Shelby Mustang, a BMW (not sure which ones, been a week or so) and the Lamborghini Diablo, which kind of made me sell them shortly afterwards (or not buy them after a test drive)
Second example being the C Class Chevrolet Corvette C6 Grand Sport that replaced the Coupe. It has these weird, flickering/moving (not really sure of the exact term for it) reflections at the area around the speedometer (the rest of the interior is fine). Also noticed the same thing on the add-on D Class C4 Grand Sport. I kept these because I can't say no to a Corvette.
So apart from those two cars replacing old ones, and several add-on cars, the pack is pretty damn good. With the inclusion of Dragster tuning, I'm probably never going to touch The stupid Crew again (also got a friend I met on that game to install TDU along with the pack so we can cruise and race around in muscle cars because they're much more fun and realistic in this game, as is every other car, with and without Hardcore Mode On. Only wish the blower on the Dodge Charger Dragster moved but eh I can live with it).