I've had GT5 for a few weeks (thank you GameFly), and I was really anticipating getting it for PS3. I'm cheap, so I didn't get it at launch. I love racing games, and the quality of the current generation makes them so much better. It's the PS3 game people were waiting for, and it was the best racing game out there. Until now. /Clarkson
I recently came into possession of an Xbox 360 (thank you Matt!), and after a weekend where we both discovered (or in his case re-discovered) the excellence of Forza 3, I picked up the much anticipated Forza 4. I must say, it is much more enjoyable to play than GT5. Both are racing simulators, however that is where the similarities end. GT5 is the professional's simulator. It more accurately simulates racing, and has a much more comprehensive training system in the license tests. However, it does go a bit overboard. In looking at tips/tricks, the first recommendation upon buying a new car is to change its oil. Wait, what? I need to do 3000 mile maintenance on my BMW M5? Um, no. I shouldn't need to wash my car after a race on a dirt road. Also, the cars can get prohibitively expensive, especially if you aren't either excellent or play it every day.
With Forza 4, the focus is on driving and racing. You get a car at every racer level, and can choose to purchase cars in between. Yes, as you advance, you get more, and with the higher classes come higher prizes, so you can get and upgrade the higher cars without having to change their oil. I like what they did with the Autovista mode, letting you get inside some of the hottest cars, with more on the way via DLC.
As a final note, both GT5 and Forza 4 had sponsorship from Top Gear, with GT5 not only having the track, but also having GT TV show clips from Top Gear. When Turn 10 sent money TG's way, that ended promptly, and they brought more than just the track, bringing Car Soccer, Bowling, and narration by Jeremy Clarkson (selected segments, including the Autovista overviews). Overall, the Top Gear experience is much better in Forza 4 because it's accessible. You can turn the game on, and after the initial race to get you into the game, you can race the Top Gear track, including in the Kia cee'd, the current "Reasonably Priced Car" immediately. To go on the track in GT5, you have to complete a challenge where you come in 1st driving the track in a 65 VW Minibus. It's fairly hard, and makes it inaccessible.
There is a new king of racing, and it is Forza 4. The fact they got out more games, with increasing quality, in the time Polyphony got out GT5 Prologue and GT5 is impressive. Maybe its the Xbox programming environment vs PS3 programming. I honestly don't know. What I do know is that Forza 4 is supremely fun, and that GT5 will be going back to GameFly shortly. And originally, I was thinking of keeping it...