I will never complain about what I wish the game had more of tracks, cars etc.
Dear God after renting and playing NFS Shift 2 I take for granted the quality that the GT Series is, nothing out there right now can touch GT5 in graphics, car modeling and physics period.
If you are feeling bored and think GT5 is lacking rent and play any of those other so called "racing sims" and if you know anything about what a real driving simulator is you will run back to GT5, we should all be thankful that we have GT to play.
You haven't played any other games, obviously.
This is evidenced in that you praised GT5's graphics even though only part of GT5's graphics are really great and much of it is sub-par to just plain terrible. You referenced Shift, and while I dislike the feel of the driving in Shift it is generally a better-looking game than GT5. Sure, certain bits of GT5 look amazing, but those things represent a minority of GT5.
The feel of the driving is the only aspect of GT5 that actually outperforms other racing games out there. Technically the GT5 car list is bigger, but if you exclude all the last-gen models and focus on just the actual GT5 models, games like FM3 have roughly twice as many cars. GT5's Premium cars aren't all that terrible amazing, either. While they do look great, there isn't any meaningful difference between them and FM3's cars.
As for feeling bored and renting one of the other games, we have a bit of a problem. Most of us are done or pretty much done with GT5 already. We pretty much
have to play something else sooner or later. 99% of GT5 players simply aren't going to be content repeating the same stuff over and over again for years in GT5. Thank God there's a rival developer that actually produces completely new (versus partially new with a bunch of recycled car and track models) game every couple years.
I was going to plug in a leaked FM4 video here but it was removed from YouTube since I watched it last night. It's adding even more content on top of the already superior amount of content available in FM3, and improvements like sixteen cars on track. Granted, GT5 has been boasting sixteen cars, but really there's very, very few events that actually see sixteen, so realistically GT5 is normally looking at twelve cars at once. FM3 generally edges out GT5 in features (five people are playing GT5 in 3D, so...), especially when it comes to online like with the amazing Storefront feature, but FM4 is adding even more.
It's really time for PD to start stepping up their game. Giving me nice driving physics but then mating that with what is effectively pretty much a PS2 game isn't going to keep Gran Turismo as synonymous with "console racing sim".
Have you recently been promoted to a higher rank in the Gran Turismo Fanboy Defense League? If not, you're due for a promotion.
EDIT:
Those games are "Ok" but are not the best even if they offer things GT5 doesn't they still fail because the overall execution of them just leaves a lot to be desired. if you think GT5 graphics are not that great then I don't know what to tell you

but GT5 are the best at this point on any console period like it or not.
Really?
I took this with GT5's in-game photo mode. It has not been altered in any way.
Tell me that's the most amazing-looking game on current hardware. Tell me that with a straight face.
Gran Turismo 5 - Honda S2000 Type V '03 at Laguna Seca:
Forza Motorsport 3 - 2003 Honda S2000 at Laguna Seca:
Gran Turismo 5 - Mazda RX-7 Type RS (FD) '00 at Laguna Seca:
Forza Motorsport 3 - 1997 Mazda RX-7:
Look those over and tell me, without bursting out laughing, that the GT5 shots look better. Go ahead and try it.