Forza Horizon 2 is an excellent game. It's probably not one for purists, I think that Forza does that better. I reckon it has the slightly "floaty" handingling reminiscent of Burnout and Need for Speed. But it is none the worse for that. And I know that I wouldn't even get around the first corner in a properly accurate driving simulation.
Forza Horizon 2 has a great narrative that has you driving from town to town taking part in racing events as you build your reputation as someone who's good with a steering wheel. If you are the kind of person that doesn't like racing on the same track every time it is well nigh perfect. The environments are very well realised and there are tons of different ones.
And now we have Storm Island. This is an add-on pack that rights one of the few wrongs with the original game. It adds lots of off road action. For sixteen pounds you can have access to trucks, rally cars and all kinds of exotic off-roaders. Along with some suitably lumpy environments to drive them around.
I've always loved rally driving games. Gran Turismo had some fantastic rally stages and while the cars in Forza Horizons 2 are all lovely and shiny I really missed the chance to sling them around in mud during a tropical rainstorm. The Storm Island add in brings the same quality of experience (driving narrative, excellent graphics, fantastic in car view, plenty of cars) to the off road experience.
If you have Forza Horizon 2 I reckon you really should get this. It's around 3.5 Gbytes of download and well worth it.