I love this game so far, it's like all my favorite things and then some. The only thing it's missing is a cop chase aspect. The best auto game on XBOX 360, in my humble opinion, is the 2005 NFS Most Wanted. However, this game obviously blows that game away. This is why I love GameFly, I'll play this for a bit, then likely buy it. It's so good, and if you enjoyed Forza, you'll enjoy this... It's Forza, with a lot more races and a lot more things to do, again, for me/in my opinion. I see myself playing this game clear through next winter.
Forza Horizon is my favorite Forza to date for a few reasons. Often times, in forza 4, many people who didn't tune their cars correctly/ have good set ups didn't stand much of a chance at all. This isn't the case at all in forza horizon. While some veterans don't like how tuning isn't in this forza, it really is a benefit for the rest of us. For people who really don't know what tire pressure works best for their car, it makes the competition more fair. In many cases, you can use the default car they give you and reach a high spot. Another feeling in forza 4 that is gone in forza horizon was the feeling that one small touch from another car would put you in last place. Surviving the first turn was almost always my first priority when going into a race. This is gone in forza horizon, while you can't stop crashers, the cars are much less sensative to other cars, which overall makes fighting for first place even more fun.
When it comes to single player , it is much more engaging than the previous forza games. Instead of going down a list or calendar you are doing races and beating rivals in order to get to the next wristband. Despite these rivals being a little bit cliche, it makes the game a whole lot more fun. Forza Horizon is a game you can play for hours and hours with free roam/single player/ multiplayer, not to mention the amazing detail in each and every car. I personally think it's definitely worth a buy, but if you can't just try to rent it, even if you haven't been to happy/successful in the previous forza games.