I really wish I could enjoy driving games more but I just find them a bit samey. The last driving game I bought was forza 2 and it spent approximately 4 hours in my Xbox 360.
Having played forza horizon at a friends house I immediately understood that it was aimed at my market, that is to say something that is bright and arcadey but without the steroids (am thinking burnout paradise) and at the same time feeling like a simulation but without the minuscule tweaking (such as forza 4). I bought it straight away and have already clocked up nearly 10 hours on it.
Each car feels unique to drive and the variety of different races keeps the interest. Graphically the world is beautiful and the decals, fonts and sounds on the menus are cheesy but in a 'doff your hat' kind of way to the arcade racers. This all adds to the fun and energy that the game exudes.