After watching all the gameplay closely and everyone's comments, here are my thoughts.
1. Artstyle is more realistic than Forza.
2. At this point Forza has better environmental details (actual foliage instead of textures, especially on the Nurburgring). Although GT's trailer Nurburgring vs. the latest day 2 gameplay has trackside details added (more bushes in certain places), so I assume Nurburgring was what they intended for the event but had to rush it a bit as they are still working on it.
3. GT is most definitely gonna improve on optimization (fence graphical glitching on Nurb I can't imagine would be left alone).
- However for 60 fps optimization, I am somewhat skeptical as PD with the last 2 installments has been not as consistent in delivering a 60 fps experience (while Turn 10 has done a very strict 60 fps performance [even in weather??? not sure]). Even GT5 Prologue wasn't a perfect 60 fps (although only a few hiccups).
- GT5 Prologue had occassional screen tearing (minor), but GT5 and 6 had significant amounts of tearing. Again, I think PD aren't as good in having strict consistent performance while Turn 10 has a better track record here with Forza.
4. I thought GT had no interior windshield reflections, but closer inspection of Mazda on Brands Hatch shows that there are interior reflections, it's just very faint compared to the obvious reflections in Forza (Forza's is too strong at all times, but GT's interior reflections have never been obvious enough at any time in the gameplay so far shown, my opinion).
- Almost all objects seem to cast dynamic shadows, unlike GT6 which took out a lot of objects casting shadows (like Pagani's cockpit reflections would show the road beneath the car, cockpit dials didn't cast shadow, etc).
- There is slight amount of sunlight leaking into front dashboard of the mazda tach/speed-ometers when in shadow), but nitpicking (Forza has same issue occasionally). Would have to do with object shadow-casting mesh (not sure what to call it).
- Still need work on certain things; Mazda's interior airconditioner outer ring material should be shiny, cockpit gear indicator almost invisible, but this is just nitpicking. Easily fixed.
- In Nurburgring race, smoke goes straight into the car itself (can be seen from the cockpit).
- Hope they add little details like the engine (if visible) shaking when revved, like the ZR1 or hot rods in Forza.
5. GT has more against itself than Forza with needed VR support and ability to stream footage live flawlessly for e-sports.
- However, Forza supports 24 cars, while up until now, GT's current build only supports 20.
- So it's comparable to Forza, but I definitely do NOT expect it to be anywhere near DriveClub and that as fact. Evolution Studios I thinks is very talented in producing their game's graphics, but they only have 30 fps with 12 cars (albeit dynamic weather/time). GT's 20 car (so far) and 60 fps with dynamic time (see below) I think means GT must have a lower overall fidelity than DriveClub. So GTS looks amazing for what it's going for.
6. Mazda footage on Brands Hatch which has the least shadow quality, but seems to have dynamic day/night change (time on dashboard changes). For those curious, the dashboard time is changing 1:1 with real life time. Same occurrence with the Mazda car on Nurburgring. Only peculiarity is both on Nurburgring and Brands Hatch, the Mazda's clock starts at 15:00, even though they definitely don't have the same day time setting (maybe the clock just measures gameplay time and there is no dynamic time change, or maybe they just haven't calibrated the clock for whatever time the track starts at). My guess is that it is dynamic time however.
7. It is only 6 months away, so I do not think the visuals can change that drastically, but the smaller details can definitely change in my opinion, for example tire marks which only existed in a later GT5 build. Same could happen for GTS and I expect it to be so. Furthermore, I don't expect the current build to be what we saw, as even tire sounds have changed with a newer build (who knows how much the current build is different).
My opinion, I think the game looks great and one of the best on consoles. In the realm of Forza 6's visuals, but with the same results as last generation (Forza 4 had better environments via higher polygon output, foliage, texures, etc., but GT overall looks better with its spot on lighting and artstyle, and on a technical level surpassing Forza 4 with what GT5 achieved in spite of 3D/Head Tracking/time change/weather change/1280 x 1080p, while GT6 had 3D/time change/weather change/1440 x 1080p.) I was also initially let down when I saw the game from my expectations of the visuals, but I think this is due to the fact of (reasons listed in this post) and that we are spoiled by DriveClub visuals. So I think GTS is actually very good in my opinion once I think about it.
Also how the heck does GTS show footage of selected car on the selected track immediately when it loads it up? It can't be video (since we can have custom livery cars), and it would take WAAY too much memory if it was in video format. GTS seems to have very very quick load times for a game like GT.