I had to comment on this thread. I am a big GT fan and always have been. I've got a G27 steering wheel with a wheel stand pro. I've been racing GT since GT3. But most recently FM has caught my eye (it was the Lambo Aventador to be honest). But seriously, for all of the fussing, hollering, and fanboy-ism, I decided to get a 360, Forza 4, and put them head to head to see with my own eyes.
My comparison is still ongoing (I have to get the Fanatec wheel to use with both), but so far all I can talk about is the AI, car selection, and track layouts/looks.
First things first; car selection and content:
FM4 has what I want. What most people want and dream of driving (minus EA's punk moves on some of our dreams). This is one of THE biggest reasons I got a 360 and FM4. Turn10 actually used their licenses to the fullest while PD kind of just ... well I'm not sure what they were thinking. A VW Bus and WWII relic as opposed to a Scirocco R and Golf R??? The Audi RS6 Avant? A station wagon over the RS5 or TT-RS? Come on, really? It's like the approach of selecting cars to ... be ... selected went like this:
Turn10 - What do people want to drive and dream of driving?
PD - What cars would we, as PD, want to have in our collection?
As for the way the cars looks (GT5's premiums I'm talking of), well this is really close in my opinion. Forza's cars look awesome. Highly detailed. But then so does GT5's; some of them requiring a double take. Now don't get me wrong. F4's car are ridiculously stunning. It's just that it should be known that the premium cars in GT5 are basically modeled with GT6 in mind. And it shows even if they were rendered for GT5. Standard cars, hang it up.
Tracks:
That's a mixed bag. Some tracks in both look just plain gorgeous. Forza blew me away with Bernese Alps, the Japanese mountain pass track (Fukaido???), and one of the Spanish tracks through the mountains. But on the flip side, the accuracy of actual tracks are badly off (Nurburgring was pretty disappointing compared to GT5's). And that's exactly where GT5's tracks shine; accuracy. Elevation change, corner radius, bumps, etc.; heck even the graffiti on the Nurburgring is accurate. Weather effects (minus the actual rain itself) and time change is awesome also. The lighting is so well done. I guess that's what makes the blocky shadows in GT5 stand out so much. Like a Bugatti parked in a parking lot full of SUVs and minivans, it's getting noticed. Bad part about tracks in GT5, old tracks not redone and just thrown in which is the worse in my opinion. Because it's like saying "we could have done it, but we just wanted to increase track count".
Customization:
FM4. Done. In GT5, if you want to paint your car, you have to buy/win a car to get a color chip. Then you have to pay credits, YES PAY, to paint your car the color of that chip. AND THEN YOU LOOSE SAID PAINT CHIP. EVEN IF IT'S A PAINT CHIP YOU BOUGHT WITH REAL MONEY AS DLC. Unacceptable. There isn't even a need to mention all the stuff you can do in FM as far as customizations are concerned. But I will note a few. All rims are available to put on any car, the engine and drivetrain swapping, actual existing areo parts for cars (although sometimes inaccurate. example: Mazda RX-8, I owned and raced one for 6 years so I know what I'm talking about), and the vinyl design tools all just awesome. Personal testimony; I got a Lexus IS-F in F4 and had the ability to swap in an LF-A engine. Priceless.
AI:
So far F4 has got it. I have had some interesting racing using the controller in F4 (I'm dying to get a steering wheel). I've used some passing techniques that seem to work well when using a controller and I have used them to the fullest (read the only techniques I can do well without bumping and going off track/shortcuts with the controller) right up until, seemingly, the game figured out what I was doing (late apexing and late braking; the AI is a sucker early on in the game). I recently had a race where the AI was doing some serious blocking. I sware that Lambo Reventon was wider than the entire track plus a half. Every corner, the AI had that Lambo just blocking racing line after racing line. Best racing I've had in a long time against a computer. Funny thing though, on the last lap, the Lambo just went off the track. It basically just gave me the race. THAT part wasn't cool. In GT5, the AI would never let this happen, ... on the rare occasion that the AI is really good (note: In GT5, I've come across some weird phenomena where it seems that the AI all of the sudden wakes up and actually gives a serious challenge). I've had races in GT5 where I just could NOT catch up to/get pass the lead two cars. I'm not saying I'm all that in GT5, but I can say I'm no pushover. I don't do that banging crap and short cuts. Case in point, the AI in GT5 is merciless. There have been some seasonal events to put hurtin' on folks.
By the way, the rewind feature in F4, I'm not a fan of. Yes I've used it, but I feel ... so dirty.
All in all, F4 is awesome. I MEAN AWESOME. I really need to get a wheel to enjoy this masterpiece. As for comparisons to GT5, well, that's just it. Compared to GT5, I hate to say it, F4 has GOT IT. But at the same time I feel this comparison empty on the side of GT5. GT5 is no where NEAR a product of the capabilities of PD.
If I was Turn10, I would be upset at the fact that PD, my biggest rival, didn't give it it's all in this round.
Sorry my post was long, but Forza 4, I am totally feeling it.