Get it, seriously you won't regret it. Forza Horizon is more of a hybrid of a Racing Simulator and an Arcade Racer. If you really want a racing sim out of Horizon, turn off all assists and you got yourself a very hard yet rewarding racing sim. Forza Horizon took out Vehicle tuning and such features that were featured in Forza Motorsport, so you won't have to worry about that, game feels like a racing sim if you want it too, and it feels very realistic, but it isn't force upon you and if you don't want to play it as such you don't have too.
Buy it, you'll definetly have your $15 worth just by driving around Colorado, the map is huge for an open world racer, you'll have tons of fun just driving around in your sweet new car, and challenging the AI racers on the street to a street race down the towns and mountains of the Horizon Festival. You'll also enjoy the silly and fun options in Multiplayer labeled "playground games", you can play fun games like King of The Hill, Infection, and Cat and Mouse. Don't worry too much about Forza Horizon being "realistic", the game is and it can feel like a sim if you want, but it has so many arcade aspect to it that it's fun. Game is extremely class and high quality.