I'm a huge gearhead, and I've always loved racing games of any type. On-road, off-road, or the rare few that mix both. I like sims more than arcade racers, but I have been known to play both. Following the rather large disappointment that was Gran Turismo 5, I was hoping that Forza Motorsport 4 would pick up where the Japanese failed. For the most part, it did.
This isn't going to be a long review. Pretty much if you've played Forza at all up to this point, you're not going to be disappointed by the latest version. It's not revolutionary by any means, but does many things to further refine the franchise. Go ahead and buy it, it's worth your money. If you plan to get any of the DLC, the $30 season pass should be worth it as well.
So... the high points? The graphics are incredible, every car model looks like it belongs in the current console generation, and the Autovista models are mind-bogglingly detailed. It's a far more consistent presentation than GT5, where loading up an "old" car model was like playing GT4 on the PS2 again.
The cars themselves have never felt more alive. Wheel hop from rear drive live axles, four wheel drifts on all wheel drive cars, wheel lift on front drive cars, etc. All translate well into your hands and the way the cars behave. One of the biggest improvements is in the feel of the track. In Forza 3 they always felt a bit too smooth. No longer in Forza 4... corners with rough patches and difficult cambers demand respect. Fail to give that respect and a meeting between you and Mr. Wall will be very intimate. Again, GT5 just can't compare here.
The car selection is still very good, and unlike the majority of GT5's cars, all of Forza's were designed for current hardware. All of them also have fully modeled interiors with working gauges.
Multiplayer is the biggest area of improvement over Forza 3. There are a myriad of options that simply didn't exist in previous games, all allowing much more control. I haven't explored all of the options yet, but it does appear that the majority of complaints were addressed.
Forza 4 is an amazing game, but it does have a few faults. The silly pre-race engine revving that you have no control over exacerbates the issue that standing starts are the only type of start Forza knows. This makes getting a good launch off the line next to impossible. It also gives AWD cars a serious advantage at starts, which is a third issue. For whatever reason Turn 10 didn't address any of these problems.
They're small issues in what is otherwise an excellent racing sim. Not perfect by any means, but certainly better than GT5's attempt.