If you've enjoyed previous GT games, you'll enjoy this one too.
The issue with loading times is being addressed, so don't let that put you off.
This is a racing game with depth that will keep you busy for a very long time. Unlike Need for Speed and the like, it's not a game that will be replaced inside 6 months by the next in the series. If you want a showy arcade style experience then look elswhere, GT5 is a solid racer for those that want a bit more than the option to customise the paint job on their car.
In that respect it's a slow burner, it eases you into racing with normal road cars and not much money, but persevere and there are some incredible premium vehicles waiting for you, all created with attention to detail that makes other racing games (on all consoles) look poor in comparison.
If you're prepared to invest your love of racing in this game, it will deliver. If you're looking for a quick racing fix along the lines of the Fast and the Furious, look elsewhere.
What you can also expect with this game is ongoing development, new features will be added along the way; GT 5 Prologue underwent significant changes during its release and I am confident GT5 will also benefit from new additions over time.
No offence to the Need for Speed crowd, but GT5 isn't really aimed at that audience. This is pure racing, not over the top special effects racing.