Great fun for hours, although far from perfect.
The controls are different again, every Forza likes to force change so it's hard now to go back to Forza4 without pressing the wrong thing. The rewind feature is back again and as before likes to rewind you to the point JUST before you can effect positive change, so if you use it you have to hit it twice. The full driving line is absolutely required in Horizon. In Forza4 I would usually leave it to braking only, but that was enclosed courses, In free roam it's easy to get lost here.
Free roaming is encouraged with 100 discount signs to find each worth 1% off at the garage, one you find them all the garage is FREE. There's also Barn Finds, where you hear on the radio that a car is rusting out in a barn somewhere, you need to find it so it can be restored. However for some reason only one of them was a car you'd likely find in a rural American barn. Most of the cars are European and every DLC pack adds a few more -Euro- cars, never much you might find in -Colorado-. I still don't understand why a team obsessed with Top Gear UK's favorite cars would base itself in the US, it probably should have been in Switzerland, Italy or Germany. On that note I still don't understand why cars we have in America are in this game to buy new with the steering wheel on the right-hand side. FORD FOCUS? That's an American car right?, pretty sure we have those. This left me very disappointed with the pathetic Season Pass, it costs as much as the game was new and didn't even yield a great car selection. The in-game selection is already severely cut-back from Forza4, and every car in the DLC is one ported over from Forza4's in-game selection. So it comes off feeling like I'm being sold content I already bought once and should have had from the start. If they were new cars maybe I'd feel different. Also, whoever did the cars has a LOVE affair with BMW, I think every pack has another beamer in it. Not all the DLC was bad, I just think I would have saved money to only buy the individual cars I wanted.
The Rally DLC was great, although the Rally tracks were obviously sections of the Horizon world with bumpy dirt in place of asphalt. I liked the few rally kits available for like 6 cars, but would have liked if they put a little more work into adding Rally gear for some of the other cars. I also would have liked being able to re-run stages individually. As it is you must do four stages in a row in each event.
The music..is Dubstep, if you are one who despises Dubstep's recent pop culture takeover you probably won't be a fan of the Dub Festival going on in the background, but you can mute it and use your music from your system's hard-drive or a connected PC. That is definitely something Xbox has over PS3. Something else you'll probably want to mute is the cheesy radio DJ, I know I muted him the second I could. I wish I could mute the clipboard girl too, she get's really old. She will get mad at you if you free roam too much without doing races. Even after you complete it all, she still nags you to buy a new car constantly.
A another place the Forza team could have made some changes for the better was the fact that this game doesn't function like Forza in that it's sort of offroad. In other Forzas taking cuts through grass is sternly discouraged and sometimes even prevented with "tar-pits" that slow or stop your vehicle when it detects them cutting a vital corner. In Horizon there are no "tar-pits" though most cars are not setup for bumpy grass so it's at your own risk to go flying over a curve. The part that needs polish there is the CEMENT bushes and small trees! I guess I'm used to Motorstorm's wonderful off-road engine where bushes would react realistically to being hit, even if it ended up knocking my car of to the side it would be better then no movement solid blocks all over the track, it's 2013 we should be past this lazy technique. I know a corvette is flimsy fiber-glass but 200+ into a bush should not equal a deadstop.
Horizon is fun for hours just to free roam around, you can get to a good top speed, I could have done without the other AI racers slamming into me constantly, and traffic often fcuks up an awesome drift, but at least there's no slow motion crashing like Hot Pursuit.
Overall I'd say it's great fun for hours although far from perfect. I'd say buy this when the price drops and get the Rally DLC. Hopefully they'll make a complete package version sometime with DLC included, jump on that if you find it.