I'll give a review.
KanyIZZY
As stated, the attention to realism is top notch and the depth is what really keeps you wanting to play more. The leveling system in Forza is set up in a similar fashion to the COD series I guess in that you're always leveling up as you play the game. As you level up, you earn more credits to purchase more cars. The more cars you purchase, the more races you can participate in. The more races you participate in, the more credits you earn to buy more cars and to tune up the cars you already own. Forza also implemented an Affinity system for each car manufacturer. This is essentially another leveling system, but it is specific to each car manufacturer and you are also awarded bonus credits as you gain higher Affinity. So for instance, you purchase the 2003 Ford SVT Corba for a series and you get up to a level 5 Affinity for Ford. When you enter another series that has a Ford car, you'll be more inclined to purchase another Ford so that you're earning more credits since you have that Affinity level at 5 already. It really is a great system that's always rewarding you for playing.
The gameplay is great in that it caters to hardcore racers and novice racers. Forza allows you play with assists which make the game easier to play; these come in the form of steering assists, braking assists and so on. The better you get at the game, you can turn these assists off and as you do that, you earn more credits for raising the difficulty. You can really tweak the game to your liking and you never feel like you're being punished when you start the game on Easy, rather you're rewarded for moving up to Medium and Hard and so on.
Forza 5 also has what's called a Drivatar. This is essentially a virtual representation of how you drive. Your Drivatar will compete in races when you're offline and will earn credits for you as well. What's cool is that you'll see the Drivatar of people on your Friend's List in the game when you race in Career Mode. It's a cool feature and makes you feel like you're racing against actual people instead of the CPU when you're doing Career Mode.
What does become cumbersome is the lack of tracks in the game. After completing a few series, you'll start to notice that you're playing the same tracks over and over. What keeps you playing is the variety of cars you're able to purchase and the leveling system. Hopefully more tracks become available as DLC to keep things fresh. As you progress, you do participate in other events other than straight races such as Chase, where you're racing against 1 or 2 other cars with traffic in your way, Bowllng, where there are pins on the track that you have to knock over to gain a specific amount of points and Signature Events where you're racing against all Mustangs or something similar to that set up. These events try to keep things fresh and although you do end up playing alternate versions of the courses, the lack of tracks does become noticeable.
Graphically, this game is beautiful. The cars looks spot on and the environments are great to look at. The damage that vehicles take is a nice touch and can sometimes deter you from hitting a wall you otherwise wouldn't care about; although I don't think I've gone through a race without hitting another car at least 2, 3, 4, or 10 times. You can customize your car almost anyway you want. You can upload your design to the game and others can download your creation. Customization comes in the form of paint jobs, rims, decals and body kits.
Overall I'd give this game a 8.8 out of 10. It's a great launch title and a game I've invested a lot of time in already. Despite the lack of tracks in the game, it's still fun to play and it will keep you occupied.