Allow me to first say, I have played Forza games since Forza Motorsport 2, so I've been through almost all of the evolutions the series has gone through (and all 3 Horizon games too). I also don't know what the length is capped to, but I'm gonna write some new stuff first and copy/paste my first impressions after 12 hours of play at the bottom.
I'm gonna get the negatives out of the way first, starting with the big one, HOMOLOGATION! The TL;DR of homologation is, specific upgrade levels (not just PI limits anymore) a car can have to keep racing closer and fairer. Sadly, it's a bit too forced, and a PITA to work around just so you can race your vehicle that doesn't qualify for homologation rules anymore. The same rewards system is there that has been in the past few, each level, you can get a car at a significant discount, but this time you can choose 50k credits (at max) or driver suits (and eventually mod packs) instead. If you buy a car from the dealer, you can choose it to be stock or homologated, but if you "win" (buy) a car from the level up, it's homologated by default. The game features loot crates, which is also controversial, but currently can only be bought with in-game credits, still gambling, but not with real money... yet. There are also a plethora of visual bugs that can really be bothersome, just knowing they're there has distracted me from driving a few times. Mostly, it's suspension not working, tires not turning, and in one case, a massively oversized rear spoiler (call me a hypocrite, but, that one is great, I hope it doesn't get fixed). Finally, the game is really laggy when it comes to certain things, mostly scrolling through your cars. It's still a single make at a time, but you can spam through with your bumpers. You can also change your car while preparing for a race and see it in the pits, but the game wants to immediately load every car, so it gets REALLY slow.
I've said this about most games in succession, when the physics get revamped, feels like more rubber is meeting the road. Well, it's more of the same, but that's a good thing. I use Forza 4 as a benchmark, because it was the most advanced for the prior console generation, and Forza 7 is about par with 4 in terms of advancements and such. It's also much easier to control the cars and use SIM steering, they'll still fishtail, but it's much easier to control them. The tuning is the same, parts are the same, PI system is changed again (but ultimately doesn't matter going through most of the game, with the exception of free/private lobbies). The sounds are also great too.
--------- First impressions after 12ish hours below
Good: The vehicle sounds are nice, seem a little richer when they're not glitching out (will be talked about later), the driving physics are also really nice, I find myself being able to hold onto and recover cars from slides a lot easier with SIM steering than past Motorsport games, and cars don't fight and lose against bumps and curbs as much. The assortment of cars and tracks is really nice, bringing back some old favorites on both fronts, and the paths to earning some of them is both kinda cool and annoying. Brings back the old days of having to earn and unlock cars. Saving up was still a little challenge, but now we got multiple tiers to work through. The game may have some long-ish loading times, depending on the cars and environment I guess, but I REALLY like that you can do things while the game is loading, AND IT DOESN'T BOOT YOU OUT WHEN IT'S READY! It patiently waits for you to finish tuning your car, selecting your mods, etc. and then it says "alright sir or madam, your race is ready" and in you go.
Bad: The audio, when at certain noisy points of the track (ambient things like fireworks), or when surrounded by a lot of cars at full throttle, likes to get REALLY choppy and cut out, and it is really disorienting. The amount of visual problems with vehicles is astounding. I've driven about... lets say 30~ cars so far... the BR-Z FE is missing its side mirrors in 3rd person cam, but they're there in 1st person and in the pits before a race, the RJ Anderson truck has very little suspension travel and front wheels don't turn, the Land Rover Series III's suspension doesn't work on the right side only, and the front wheels don't turn. The Toyota Baja truck has the suspension travel of a typical street car, so you frequently see light under the wheels. How does this even happen? I'm scared to drive the rest of the cars I've collected on my trek to level 32. The drivatars, although haven't had a chance to learn much yet, act like you don't exist. They'll shove you off the track, run into you, slam on the brakes for no reason right in front of you, and this is with aggression turned OFF.
Hybrid of bad/why: When you select and use 3 mods fully, they disappear, and you're stuck at that screen for like 15 seconds. If you use 2 and there's 1 remaining, doesn't freeze, only when you use all 3 (or possibly use a single one fully, haven't tried only 1). Can't restart from a race, you have to quit and go back in.
Why: The shopping cart system didn't make it into the game. Everything defaulting to homologation unless bought directly. Not being able to actively tune your cars in free play. Having to jump through many hoops to test drive your car. Launching the game with the horrible new VIP system, which they have since addressed, but going through with that idea was very *omitted* stupid, even for Turn10. Joining a multiplayer lobby and being thrown out of the party unwillingly.
All and all, I'd say like 5/10, probably the worst one to come out in terms of quality, especially being the SEVENTH Motorsport game in the series.
Also, a personal gripe, they still haven't fixed the angled cockpit camera. Looking forward, you're looking down. Looking left and right, your camera is tilted forward like 15 degrees, and looking back, you are staring at the sky.
As a final note, wait for price to drop or get it on sale, don't pay full price, they don't deserve it for this quality.