Those clouds and lightning in GT6 remind me a lot of Red Dead Redemption and now GTA V, they do look gorgeous indeed, I wish the rest of the sky wasn't so dark though, the gradient is nice but it goes too dark too fast. Still, what matters the most to me is performance and picture quality, GT5 outputs a much cleaner picture, it looks sharper and it's more stable. I don't think GT6 is absolutely horrendous but if we are all honest, it's nowhere near what Gran Turismo should be by now, there's always something holding the series back and worst of all is that they're the stupidest things you can imagine that they just refuse to fix. Even if GT6 is indeed a great game, I'm sorry I won't give it a chance. I'm voting with my wallet.
It's brighter in game. The camera reduces exposure when you point it at a bright object, and I also used an EV value of around -1 or -2. It's still a bit darker than in GT5 though, at least at that particular time of day.
Sure, graphically there are tradeoffs. There's only so much that can be done on a console, especially one that is quite old by now. For someone who wants performance over anything else they should probably have killed some darlings and gone for simpler graphics. I find the performance perfectly alright, but my TV doesn't do more than 720p either and apparently the performance is more solid at lower resolution.
If we're talking about issues with the game, I certainly don't think the graphics is one. It might not be a 10/10, but it's definitely a 9/10 (9.5 if you consider it's a PS3 game). And it's probably an area where they already focus hard. I'd be more concerned with gameplay features, because although the graphics are great and the physics are great, the structure of the career mode is simple and unexciting.
They have a huge library of cars, a great variety of tracks, they have fuel consumption, tyre wear, weather and time change, mechanical damage (that's really on a whole new level compared to GT5!) and yet the career mode feels like they're only using 1% of all their assets. Short races, few races, no damage, no tyre wear except for the last batch of "endurances". A huge amount of cars are never used, or used only once. Let's say, for instance, that I find a great car that I really want to drive a lot. Unless it happens to be a high powered race car, the only place I can really use it is in the lower stages of the career - where the races are the shortest and easiest.
It feels like the only place where the assets really come to use is online, but there you have to depend on finding others that wants to do the same kind of events that you are interested in. If it's races shorter than 10 minutes in 550 pp cars with racing soft tyres and no damage, then you might find a few. If you're looking for 2 hours of endurance in 400 pp cars with sports hard tyres and full on simulation, then you'll probably have to race alone.
So that is where GT6 falls short as a game if you ask me. The graphics would be the last thing I'd think they need to work on.