I'm curently playing Forza 3 Ultimate Edition. I like racing games and played a lot of them since Formula One & Gran Turismo on Playstation. This Forza 3 is for me the best racing game but it doesn't mean that it's perfect.
Forza 4 has been announced at the E3 and will improve the game, but, from my point of view, it's always missing something to be the ultimate racing video game.
For me a racing game must be related to two things : cars & racing competition. Let me explain.
Cars
People who's playing that kind of game like cars, like buying cars, like having lot of cars in their garage, like washing them, like tuning them,...
In Forza 3 you can decorate and tune your cars and... that's all. Ok it's the main things but it could be better.
Your garage looks like a list of cars. If you want informations about your cars (the circumstances of the making) you must go to wikipedia. However it's something that will be fixed in Forza 4 with the [youtube=J8peKqHrT54,,853,480,]Auto Vista mode[/youtube].
Most of the time you don't have to buy cars because the cars you unlock during the main mode allow you to participate to most of all the races. Buying cars, choosing the one you dreamed of it's a big part of the pleasure in a car games. Seeing races you can't participate in because you don't have the right car in your garage it's interesting. It tease to player, give him the motivation to earn more money to buy the right car.
I understand this car unlock system because it's rewarding and make the game more accessible (the game show you automaticaly the right cars you must choose for each race). BUT I think they've gone too far. By making it more accessibility they've removed all the teasing, and made the main mode boring after several hours.
Gran Turismo doing this right by teasing a lot. However the bad thing in the GT series is that you must do several time the same races to earn enough money for buying the right car for the next race. In fact the good solution would be between GT and Forza.
For what I kown about Forza 4, they want to make it even more accessible by proposing to the player only race you can participate in with the car you have. I'm afraid it's not the right solution.
Racing
In what Forza is good is in the racing experience. The track looks realistic, the cars behaviour seems real, the oponents AI is clever and agressive at the same time. Your tires can go bad, you can ruin everything in your car if you hit things.
What's missing? Changing weather & the excitement of the race. Doing qualifications, brandish your trophy with a big bottle of champagne is a big part of the pleasure in the race. In Forza it's a bit too impersonal. It's a menu page who congratulate you with you position and the XP points you won.
Turn10 know what to improve now :)
I've spend some times to make it looks good
PS: all the screenshots here are made by me (the jpg compression of the screenshot system is sadly a bit too high). I've made a replay that you can see below, but the system is not easy to use: You are able to upload more than one replay from the game and, because it's in wmv format, you can't upload it directly to YouTube.