Doesn't do the Forza name justice
Where do I start? umm... The arcadey feel of this racer is 100% proof positive that it is NOT a Forza game. It's more like Need For Speed XVVII at this point, with a garish color scheme designed for bros who wouldn't know a Jaguar XJ from an Aston Martin or a Porsche 914 from a Triumph (or more likely, "old crap" in their words.) The single player NEEDS to have the option to change cars without fast traveling twenty minutes from the race I was checking to see whether or not my car would be adequately tuned for (or pay credits to use an outpost) Also, the car selection is absolutely horrifying (although I was pleased to see the "barn find" mechanic, that's a neat way to get access to some of the more classic cars in the game, and my fanatical obsession with Lancias has been sated somewhat--but where's the other classic, the 037?)
The driving physics feel like they were designed by an 8 year old who got tired of not developing the reflexes to succeed at any other racer and decided to make cars turn a hairpin at 100mph, with under- and over-steer not being adequately modeled in the slightest. The open-world game design is okay, but it's offset by the abysmally fudged physics. Opponents (specifically AIs) very often make slingshot recoveries.
There are some redeeming qualities about Single Player that give this game a 2 star rating in my book rather than a .5 star. The open-world, "go explore" setup is new and fresh to the franchise. The barn find concept is pretty neat, and not knowing when the next one is available is neat. Showcase events are fun, at least the ones where you're racing (random aerial vehicle vs. car). Off-asphalt racing is a first for the franchise, and it's really not as fun as I thought it would be. Gran Turismo did dirt AND snow racing far and away better than this game.
And now we come to the biggest problem of all. Multiplayer. Ho. Ly. Crap. Other than voting on the car class of the next race in the lobby, MP is quite possibly the worst I have ever seen in a racer. Forza 4 had lobbies that were for one game mode and one game mode only. Horizon's "playground" lobbies (I played mostly Virus tag and Soccer in 4) rotate between King (which is Tag Keep the IT to people who play 4), Infection (Virus tag) and Cat and Mouse. I *hate* Cat and Mouse. And I really don't like Keep the It all that much. Let me have an Infection lobby in the "official" playlists so I can join other players and just play the game mode I'm interested in. The lag is awful. I have a fast connection and usually don't get players driving on top of my car or whipping around 80mph corners at 150 and bouncing up and down halfway through the pavement in 4. This was all over in the MP lobbies I joined in Horizon. There are entirely too many hiding spots on the maps that come up in Infection and King which wouldn't be bad in and of itself. But you can't see the location of infected players on the minimap when you aren't infected, and you can't see the location of uninfected players when you are.
TL;dr: The good: Offroad racing. Showcase events. Barn finds. Open world design. Voting on next car class in MP.
The bad: Fudgy physics engine, slingshot opponents, randomized mode MP lobbies, terrible lag.
The verdict: This game does not deserve the Forza name. It's a Need for Speed clone with more interesting cars. I know it's designed to get new blood into the Forza genre, but all it's accomplished is ruining the franchise with a steaming pile of crayon physics and badly executed MP. If you know about what Forza is, don't buy this. If you don't know what Forza is, buy Need for Speed or Ridge Racer or whatever NFS clone is currently around. Don't buy this.