I've been dedicated to the Forza series since Forza Motorsport 2 years ago. I have owned every single Forza since then and have put at least 100 hours into each and every one, peaking with Forza 3 at 1,100 Hours.
I say this because I know what Forza is supposed to be. Here are a few of the defining features of the Forza franchise (opinion):
1. Any Car, Any Time
From Forza 3 to 4, the ability to climb into any car and just drive has, to me, become a core part of what makes a Forza game, as well as giving some kind of value to downloadable content.
2. Huge Selection
The review of FM5 Goes over this briefly, and that is the painful lack of staple vehicles, but even more-so, tracks. Key tracks that have followed the series since number one are inexplicably missing. Nürburgring, Fujimi Kaido, Maple Valley, and much more. The reasoning behind this? Possibly the fact that Turn10 has been laser scanning the tracks for FM5 and was unable to get them all finished before the Xbox One release. Forza 5 is not a simple game, being a 3d modeler myself I understand the time implications of recreating that number of cars and tracks in such fidelity, nevertheless, Turn10 has sacrificed what is to me, the most defining feature of the franchise, to commercialize upon a day one release.
Forza Motorsport 5 is missing this rather plainly. If you look anywhere slightly beyond the surface, you will find bugs and missing or incomplete features. Small examples being tire flex not being modeled correctly, and a free play mode that is nowhere near as comprehensive as in any previous games by Turn10. These do not detract from the fun of the game all that much, but they are a clear indication of Turn10's commercialization, if micro transactions and monthly DLC weren't enough to convince you.
So what do I think of Forza Motorsport 5, the premier sim racer in the new generation of consoles? I love it. It is an amazing game that deserves praise and your money if you even like racing a little bit, but it comes with a disclaimer for hardcore fans of the series like myself. This is indeed a great game, but it is not the Forza I have come to love over the past five years.