You may feel that the graphics are great, along with the physics and online. But to some like me, there are room for improvements. In fact, I have problems with just about every track graphics wise. Those that don't have weather and/or time changes (which in itself is already an absurd notion, considering tracks like the Top Gear Test Track lacks any changeability) have too much contrast, i.e the sunlight is too bright, making replay photomode very "one directional". You either take the shot at an angle where the car is lit well by the sun or take a horribly shadowed shot.
Even in the very few select tracks that DO feature weather and time changes, it is far from satisfactory. The reflection of a wet track when struck by light, for example, exists only in SSR7. And that track is pretty much redundant if you have SSRX. Not to mention it lacks pit stops or any scenery worth mentioning. Your car does not look like it gets wet in replay photomode either. And what about the area in your windshield that isn't covered by your windshield wipers? They have droplets lingering on them when you're racing in cockpit view, but simply disappear altogether in replay mode. Or what about the fact that there are no fireballs involved when two Jay Leno Tank Cars collide on the Mulsanne Straight head to head on the Le Mans circuit? I highly doubt reality would be that kind to anyone who tried that stunt in real life. And in a game that bills itself as "The Real Driving Simulator", I want those fireballs, as immature as it may sound.
I've also heard a lot of complaints about the shadows in the game. And rather than explain in text, have some pictures.
I can't refute the physics being great point, because I've yet to drive a car in real life. But some flaws I noticed are that the acceleration in the game just spikes from half to full throttle after a certain point in your input, even if you're using the L or R2 button. Not to mention, I've heard that GT5 lacks the pedal feedback feature for when your wheels are about to lock up from braking. Or what about the confusion with the brake balance? How you could set it to amount to a total of 2 or 20? How every car initially comes with a 5/5 brake balance? Does that figure represent the car's factory fresh braking performance? Or altered so that the front and rear match?
Online play has been pretty awful for me. I've had a billion connectivity issues with friends, let alone strangers, like me not being able to enter their lounges nor public rooms. Or how there is no matchmaking, nor better filters like PP and the like.
Of course, that's just my conflicting opinion on what the OP stated was already amazing and needed no improvement. There are still other issues, like the menus taking forever to load only for you to spend one second using them. Or how standard cars only get 3 equally ugly and obnoxious rear spoilers with none for the front. Or how even some Premium cars suffer from the same problem. How we can't customise the looks of our cars much at all. How there are no paint previews for one time paint chips use. There are just way too many issues and room for improvement to be simply amended via patches and DLCs. In fact, hoping that GT6 would fix any of these issues is just wishful thinking at best, knowing PD and Kaz's indifference to the community.