Okay, here's my general opinion after one night with forza, which will most certainly change as I get more time with the game.
A.I.
It's pretty good, surprisingly, but that's not to say that it's revolutionary. For the most part, it still follows a line, however it's stated in our press release that there are still bugs in the A.I. It's pretty good, however, with control of different cars. It doesn't display the same problems that other racing AI suffers from, i.e. over powerment of cars, and sliding out. While the race line is still generalized for all cars, they follow it much better rather than falling out in stronger cars.
Visuals:
I didn't like them. LOL. I know I'm going to get nicked up by everyone, but in my opinion, they were a bit...well slow. I know everyone doesn't really car about 30fps..but it was driving me insane. Especially in the 8 car events, I experienced siginificant slowdown. While this will more than likely be fixed in the final version, it was pretty buggy in this build.
Control:
Phyics were good, on par with GT4 IMO. HOWEVER, you need to understand that Forza does have a different feel due to the tire model. The physics are great, and from the play I got, felt on par with GT4, but it shines with the tire model. Wear is a bit better, and each car displays different wear.
On the topic of temp. etc. There was a difference, however, in the build it felt like it wasn't significant, nor did it change greatly in different temps.
Another thing I couldn't stand was the control (button wise). It was driving me literally insane. I just did not like shifting with face buttons rather than shoulers. It was odd to me, and felt rather uncomfortable. I didn't change the controls however, so it's not really a gripe that I should complain about. The analog sticks felt extremely too sensative though, while the d-pad was undersensative.
Sound:
Sound was good, but still buggy in the build. There were several cars that were on different sound levels (even race cars) and sometimes the whine of the turbo, or tire squeek, was too quiet, or extremely loud. These are just early bugs that I'm sure will get fixed in the final product. Overall sound was good, though some cars sounded overly beefy..
LOAD TIMES: IMPORTANT.
There have been complaints about load times, but it needs to be understood that the optimization of load times has not been done. When it is, I expect load times to be at least 25% faster than they are in this build. So load time complaints should be taken with a grain of salt.
All in all I can't give a huge impression yet, but after more play time I will. So far it's a pretty decent racer, with a few bugs here and there, but that's expected with a preview build. I dont' think we'll see this game in april though, I just don't see it happening. It's going to take time.