Having spent almost three weeks solid with Forza 4, I have my own perspective to offer on all this, and the quality of the two games.
After racing in F4 and going back to GT5, the game feels much "safer." The cars don't feel quite as alive. There is also kind of a "sameness" with many of the cars in the same class: sport sedans, small mid-engined, AWD, etc, but more on that presently. They're more sure footed, more solid, more in contact with the road, especially with ABS at 1, which seems to give you all the aids on at one or two ticks, curiously. Disable ABS, set the Brake Balance lower front and rear, add one or two ticks of Stability, maybe the same of Anti-skid and or Traction Control, and now the cars are more of a challenge, and you can spin out without really braking or pushing the car hard around a turn. Set everything off, and you'd better have a firm grip on the wheel.
In may ways, Forza 4 is exceptional, and has physics on par with a racing sim. But in others, it's like some hobby build that's just not right somehow. When the game first starts for you, like Toca, it throws you into a race out of the blue with a Ferrari 458 I think, an automatic with all the aids on. It's quite an eye popping experience, giving you such a powerful car and in such a scenic setting as the winter Alps and a nicely curving course, and most decent racers shouldn't have any trouble winning. It even lets you start over if you mess up. But then the real game begins.
While F4 feels more alive, and the cars have a discernable mass to them, this isn't necessarily a good thing. Real cars just aren't quite this wobbly, especially on racing suspension. They all feel like they're on springs of various stiffness, and is no doubt the source of complaints that the cars feel floaty. Also, the cars are all ridiculously LOUD! even with the audio balance set to favor tires. Every car you race whether stock or not sounds as if it at least has a V8 and a racing muffler - or no muffler. While others have no problem with it, communication to me through the MS FFB Wheel is poor. Often it feels like a big hand controller. The tires aren't communicating how well they're gripping until they're about to lose it, or overload in turns without much warning, and then they squall loudly. What's more, I experience an annoying tendency of oversteer in every car, in which it wants to keep turning around curves above some certain speed, 50mph or so. It's as if every car has a large mass in the rear, and I have to jerk the wheel or stab the brakes to make it stop. Even the 3D perspective is a little confusing - I race in chase view, the only one that works well for me. So between that, the wobbly suspension, oversteer tendency and the reluctant tires, taking turns is a bit too experimental. If that wasn't bad enough, the bots are terrible, often as bad as GT5's bots in braking too early and hard approaching turns, but then they also drive recklessly, late braking to get ahead of you, and able to succeed (cheat) where you might not, and they will intentionally ram you, bashing you off the track in some cases.
In lower powered F and E Class cars, the kinds of sports cars we mortals tend to own, I could manage okay with all the aids off, but as I went up in classes, the cars just got to be too unstable, and I began to think of quitting entirely after just a few days. But that opening race suggested I try it with aids on, and it was somewhat better after that. Unfortunately, brake assist does little more than slow you down when you're trying to race aggressively, and ABS barely works at all. The suspensions are still too wobbly and the tires still don't communicate until the last minute, so you have to do a lot of racing to really get a feel for what the game demands of you. Doing some time runs with the dynamic racing line on with all the tracks isn't a bad idea, which is something I intend to do over my vacation.
And this all culminates in the big difference between these two games. While the Forza fans no doubt adore F4, and you'd be well advised to not be very critical in that other section if you want a pleasant visit, it's just strange to me. It doesn't feel or the cars handle like any game or racing sim I've ever experienced, other than Ferrari Challenge. Racing in anything above F Class just isn't intuitive. You have to fight the game as much as the race, at least many of us outsiders do, and between the wobbly cars and bashy bots, you will bang up your car in every race and get to enjoy the marvelous damage modeling, unless you happen to be out front way early.
Contrast this with GT5, or just about any racing sim you care to name, and there's a huge difference, though I'm going to stick to Gran Turismo. Cars tend to behave the way you expect them to. You aren't fighting the game as much as the car. You can hear the tires and juge their mood pretty well, and because of this, you "feel" the car much better around turns, and feel more in control and connected to the vehicle. The 3D perspective looks more real to me. You can attack turns without feeling lost or numb, you can hit apexes more reliably, you can aim for bumper strips, you can exit turns with authority. The cars speak to me more clearly, and I can just darn well race.
While cars in similar classes and builds feel similar, I think this is proper. Considering that most of the differences in real world car feel comes down to... well, the feel, when you have no direct sensory experience of a vehicle, you can't expect vast differences between all the cars. While it can be debated how well Gran Turismo models proper variations in different cars, I think they do a reasonably good job. Forza 4 doesn't get carried away with differences to me, which I appreciate. And frankly, I'm growing to loathe the engine racket in F4, prefering the "vacuum cleaner" sounds in GT5. Which if you listen to replays with all but the hottest supercars or race cars, the bot cars all sound like vacuums themselves.
I also have to comment on how much I've grown to despize the Top Gear license in F4. I couldn't believe it when "race events" ammounted to a stint of bowling on the Top Gear Test Track! And I haven't gone anywhere near Autovista yet, because I'm just not very fond of Jerry, and I've seen YouTubes of it, not all that impressive to me, and not too many cars either.
Still, both games have their appeal for me right now. I enjoy how viscerally alive the cars feel in Forza, even as they vex me to no end on how badly they misbehave, or how extremely hard it is to get them to do what I want. I have a few replay examples in my Storefront of the trouble I have with the oversteer factor rearing up in turns. I would have a fourth, in which my F430 politely tries to steer itself off the road, but evidently "F430 03" gets blocked by a decency filter, "bo ob" I suppose. It is the new game, and I do want to complete it, which I didn't do in F3, in order to collect some nice rides and race mod them with custom liveries.
However, GT5 is my dessert. While safer, it's such a relief to not find myself fighting the freaking universe. It's nice to feel like I'm in control of a car that makes sense, that more or less does what I want, as my PC sims and real cars do. The bots don't pick fights with me, they race, and in Arcade Mode, the higher difficulty bots are fun to race with. I don't need to face tard kids online for a good race with a full field of cars. And there are TONS of cars to choose from! Sorry Standard haters, I love them. I haven't had time to play with the DLC yet, having been sidetracked by my MMO time in Anarchy Online, as well as Battlefield 3, way too short a game. But this friday, I intend to spend some quality time with it.
Sure, I'd love for GT5 to feel more daring, challenging and lively as Forza 4, and have that marvelous selection of bodykits and that delicious Livery Editor. But I'm just not groking that other game compared to "The Real Driving Simulator."