Wow. First gameplay, graphics, and then console specs. I stopped reading by page 21 and skipped to the end lol.
Lets see...
specs: Xbox is better, live with it. I missed my xbox when I played Splinter Cell

T on the PS2. Holy crap does the graphics suck.
gameplay: Forza is a newcomer so it definitely has something to prove. Initial review of Forza physics being better than GT4 should be taken with a grain of salt. Mainly because emulating the driving feel on a joystick that vibrates hardly does actual driving feel justice.
I bought GT4: Prologue with the Logitech 900 degree wheel. I couldn't believe how much of a difference it made. After playing GT4 for a week I couldn't play GT3 because it felt so different. This is a major issue with Forza and xbox. Unless MS or someone makes a 900 degree wheel for the xbox GT4 WILL have a superior feel to it. I could care less how it feels playing with a controller because frankly it's utter crap. This is my opinion and for those who can't afford the wheel, this might be really important for them. Now Prologue blew me away and now I hear the updated engine is alot better than Prologue. There are some issues as there is no road feel at all in Prologue (which I hear has been resolved). The wheel doesn't really let me know when I'm at the limit, only through the sounds of tires squealing and my back end coming out do I realize I'm gone, but by that time it's too late. So road communication is one area that I thought needed improvement. BUT for what it can do I was blown away.
Forza definitely needs a ffw to compete seriously with GT4. I don't doubt that it's turning out to be a great game, but I think in order to be taken seriously against GT4, a wheel is a must. I don't think a fair assessment can be made without it.
graphics: I'm amazed at what PD is able to do with such little to work with. Just think about what they can do if given xbox capabilities!

I believe that GT4 has better texture work than Forza. The reflections off the cars and general environment the Forza definitely has the advantage and this is where xbox superior capabilities shine. Forza also reminds me alot of the graphics "feel" of Top Spin. Don't know if anyone played it, but the graphics had this strange, unnatural feel to it. Looked great, but didn't quite seem right.
Forza also definitely looks better close up, due to the large # of polys they're using, but when looked from afar GT4 looks more realistic.Key word here, more realistic, NOT better. GT4 has this grittiness and natural lighting that Forza is lacking. Forza cars just look too clean, I don't know how much they fixed this now but this is based on pics that I saw on the thread up to page 21.
Xbox owners who love driving games will buy Forza. PS2 owners will probably not see the need to go pickup an xbox go get Forza unless they got the $$. One thing I will miss is the supercars from GT4. I would love to drive a Ferrari 360 and see what it's like. For some this is our only way to even experience these supercars. hehe