GT5 is flawed in two major categories, and no features, content or additions to the game are more important than these two things.
1. Stability. This is one of the most unstable games I've ever had the misfortune of trying to play a lot of, and I've played a lot of GTAs, Elder Scrolls, RDR and so on, so I understand that with expansive large scale games tend to come more bugs and glitches, but on a day to day basis, GT5 freezes and crashes far too often. People can't load tracks and are forced to restart their systems on a nightly basis in our online testing and racing. Just now, trying to exit from a B-spec race I was met with another black screen and the sound of cars still racing on track, which required a button reset of the PS3. This is not exclusive to online or off, any specific tracks, cars or game modes, nor any one or few gamers. The game is just too complicated, or too poorly designed to function propelry.
2. Efficiency. Never have I spent so much time in loading screens... or waiting for the paint list to load... or the car list to load. Just starting the game up requires you to wait for the game to load the background animation for a redundant menu screen. It's all very painful and wasteful.
Just look at how the paint system works. It boggles the mind how poorly it works, and how far from common sense you have to depart to get to the system they implemented. On top of that, when you have a large quantity of paints it becomes very slow to load and sort, and it just shouldn't be that way...
I love this game, but after over a year of it I've lost out on a great deal of actual driving time because of glitches and long load times. The agonzing wait for GT5 to arrive has been surplanted by the agonizing wait for GT5 to load, and the frustration that when it finally does, it freezes up on your way back to the main menu.
GT5 is now really only appreciated by long time GT5 fans, and among them it's really only the patient who remain. I'm a patient person, but now when GT freezes I don't usually bother going back in to finish what it is I was doing, which is sad.
I can already hear the backlash that I'm a demanding, impatient, typical whiner who doesn't appreciate the work they do, but that's simply not true. I've supported this game for a long time and I'm just calling a spade a spade. PD needs to focus on Stability and Efficiency for either GT6 or GT5 3.0, or they will continue to lose ground to their competitors.
All the content in the world won't save you from flawed design, but when your design is solid it's a lot easier to focus on adding content.