Less to do with them being broken and more to do with the fact that reviews have been and always will be nothing more than opinions. 

And Eurogamer Germany a 10/10

Edge gave it a 7/10 http://www.edge-online.com/review/forza-motorsport-5-review/

Looks like my 80-85 meta prediction was right, I knew 90 was to high

Wow. Dem harsh critics.

I get the feeling that reviews for next-gen games in general are intentionally low this time, on both platforms.

Well GT5Prologue doesnt pretend to be a full game and charge full price also. It is a taster/introduction for the full release of GT5 and it retailed for $30.

But ki is free and its getting hitvfor lack of content lol

I dont think so it has less content and a more boring campaign than the last one so it gets a slighly lower score, seems fair. 

Its a launch game, as much as people like to deny it, it will of had corners cut to get it out on time like all launch titles. 

Im not sure how Killer Instinct can get downgraded for a lack of content while Forza 5 gets great scores despite a lack of content.

Granted, different reviewers and what not but it sure shows the lack of consistency in the enthusiast press.

yeah I too am really surprised, with all the praise Forza games get and all the hype for 5 I at least expected an 85 minimum. Was more expecting 89-91

Exactly, it's launch game and there is a *lot* of diversity. And I am not talking about this game in particular but about the next-gen games in general. But as you mention it, given the lack of content a 83 is impressive!