I gave a generous 80, though I could've justified a 70 just as easily. The offline/online physics issue, the inconsistent settings screen (some cars seem to benefit from "backwards" tuning, others, not so much), the simple tire physics... it's an incredibly ambitious game, but by that same token, there's a lot more that can go wrong.
The over-reliance on last-generation assets is a big one for me, and the lack of more community-building features is too now that I'm used to things like a Storefront, Auction House, and livery editor. That all said, PD has been very good with supporting the game-post release (arguably because, to a large extent, it needed it), their new content is of the utmost quality, and when they do things well, like the Nurb 24H with time and weather change, well, they do it better than anybody else. But the flaws and shortcomings are more noticeable in this iteration than previous games, and I think the score should reflect that. Yes, it's done far more than the installments before it, but that alone should not guarantee a higher score - times change, and in some departments, GT isn't changing fast enough to keep pace with them.
Still a very good game, of course, but the undisputed champ it is not.