What about GT4? That if I'm not mistaken is loved to death. Probably on the same level as GT3.
I'm sure it is, but after A-Spec the overall reception had still been steadily declining. The first three games are still the only ones with 90+ review aggregates.
4 was undoubtedly great, but not quite the triumph that A-Spec was. Then we had GT5 Prologue which was understandably more a physics demo than a game, but even 5 had significant technical shortcomings that stood out more than ever seeing as it was supposed to be the PS3's grand slam.
6 had the oppportunity to correct the major issues (bloated menus, low quality sound, filler cars, damage models, etc.) but really only the first point was addressed to any significant degree. I still play it because overall it feels like an improvement, but I would've loved to read the first PS4 GT game would have a full suit of offline features with online as a bonus instead of the main focus.
The advances in sound, car models, physics, photo modes, etc. are terrific so far, but can't help but feel they needed to scale the dynamic details back to accommodate a smooth online focus along with 4K/HDR.