To buy or not to buy

I am a huge fan of the Forza series, can't decide if I should buy this one though, I still have FM3 sitting on my shelf waiting to be completed. I might wait for a discounted price tag.

I have pre ordered forza 4 so should hopefully get it tomorrow or sat, couldnt decide weather to get it straight away or not as wasnt sure how bigger different's there was going to be from forza 3 but been watching alot of reviews on youtube and it looks really good, am a massive fan of forza also.