If I were you I would hold on for a few days before you make your choice. I haven't played GT5 yet, but I have played Forza 3 extensively. I was hoping for Forza 3 to better than Forza 2, but in regards to certain aspects I was dissapointed. What I can say is that GT5 does have a few things that Forza 3 does not, like a weather system, dirt tracks, karting, and night racing. Forza 3 is still a great game, but it just felt to me like a Forza v2.01.