If you only have a PS3, then bit-tech.net would recommend you get this game to tide you over until the full release comes along sometime next year. On the other hand, if you've got an Xbox 360 as well, they would recommend that you stick with Forza and PGR as they'll give you more satisfaction in the meantime.
As a demo, it's a great way to show what's to come. The only problem is, it leaves you feeling unsatisfied with what you've got and impatient to wait for the final release. Should gamers really be paying for a demo in the first place?