GT5 has fantastic assets. But as a game design it leaves a lot to be desired.
Specifically those menus are such giant boner killers. I mean... they're not super terrible, but the fact they've optimized for presentation over usability and speed makes the game incredibly frustrating given the scope of the game.
I usually only play a race or two at a time before turning it off. Or I just take some car out to some track and time trial it until I'm tired. One of my favourite thing about GT in general.
The progression system also leaves a lot to be desire. Second hand cars that are required to complete races, frequently not been available (especially some of the more esoteric requirements) when you need them.
If it was upto me, I'd bring considerably more value to all the assets by organizing race themes and 'story lines' into the campaign mode.
e.g. a rally season - rally only cars, you're given a specific car, with allowance for specific upgrades, you get a character name, there are story rivals, and there are simple cutscenes (pictures/words/voice overs) between races that develop the story, with some simple requirements for races (beat x time, get in 1-3 spot, etc).
Gt5 is just so frustrating to me, because I know it wouldn't take a lot of work relative to the amount of work that's already been put in, and continues to be put in, for the game to truly shine - as a game, and not just as a car collection simulator.