I bought Forza 5 in the January sales, It really is poor compared to the previous games. On the flip side I thought Forza Horizon 2 was awesome.
Just imagine how poor it was on launch day! Some of the problems were related to the underlying APIs for things like matchmaking being bobbins after Microsoft decided it was a digital hub and not a games console, then doing a massive about face. To be fair the entire Xbox One has had a massive amount of development thrown at it in the last 12 months on the gaming side to get back on par with the PS4, to the point that kinect is basically a white elephant having had all it's resources cut off.
Fair play to T10, they nullified the microtransations and readjusted the game mechanics quite early on, even if it's a tad easy now. They also didn't charge for the tracks. Just a shame they didn't add a lot of the missing features back in. There was a pile of simple stuff a couple of interns could ported over from the older Forzas in a couple of weeks.
There's a laundry list of things what's left of the community want, and it hasn't changed in 5 years :
Day/Night
Weather
League/Tournament facilities
More tracks
Enduro Races
Rims/Bodykit options not stuck in a 2004 time-warp.
They also need to re-add the community features that worked so well on the 360 titles that got stripped out to make the launch. Auction House, Car Clubs and the storefront being the main things. Lack of these in FM6 for whatever reasons (time, XBL API issues or even stupidity) and it's the series will be dead to the existing community. They won't be coming back.
Until I see proof otherwise, I'm convinced T10 will screw it up. Unfortunately.