Forza is a special saga for MS. From a bussiness perspective Forza has more related with having "MS´ Gran Turismo" than anything else. It´s just a marketing goal for the corporation, I think -T10 is one of the few firts party studios that are still active. The sales are far from impressive (in comparison with other genres, more suited for the american public, perhaps), but T10 still receive support and the evidence is this F4.
With this in mind, is easy to understand the extreme verbosity of the team. It´s just big scope strategy, and they´re obviously in line with this vision. The point is, in any case, balance the lineup, or at least create and transmit the idea of leadership in the genre.
The other approach is the game itself, a good game, no doubt, maybe a bit more accesible (some would say "modern") and with the clear idea of clean the interface and being elegant, colliding with the approach followed with PD and the cluttered menus from their last game.
The thing is that PR is very influenced by the corporative goal, and as a logical consecuence the videos are extremely focused on "suggest" and, being honest, and after playing both sagas extensively, the advertisement video is a good example of contermeasure of the variable clima, snow, dirt, night races of GT5, but without compromise; "We´ll be there, but we don´t show how it will be".
The effect is inmediate for fans (Forza series now have day/nigh races, snow/dirt, etc), but in fact we haven´t see anything yet.
Once again, Microsoft is a superb example of marketing procedures and succes.
Being more technical, taking into account that F3 was extremely stable, they have room for sure in order to improve transparencies, particles and Fx in particular, which weren´t impressive, but the problem is what they see as Fx.
GT5 (obvious reference) has a no-compromise approach, with rain being massive rain, light being night/day complete and dynamic cicle, multiple lightsources allowed and so, but with obvious problems with performance and some ugly pixelated effects. They may well be more conservative but at the same time more cohesive and show wet roads but with fewer smoke, or transparencies for water splashed, more "clinic" again. And it will pay with reviewers that usually go for the obvious faults and tend to forget why those faults happened (1/3 more resolution being one of such things).
PD has dropped the ball offering the game clearly rushed. As Sony, I would consider the launch of a "finished" GT5 for next holiday in form of GT5 goty or something like that. It would sell in spades again and will benefit the image of the studio.
In any case, the trumpets are singing aloud and we have a promising duel for supremacy in the genre, excellent news for car lovers...
Ironically for PD, F4 could benefit of the "relaunching" of the genre due to big GT5 sales. We´ll se. I just hope they release some ingame direct feed soon, not only the detailed photomode they gave us last year. At least, the visual tour with kinect from the ad is pure Forza essence: elegant and clean. Very well done for sure.