A contemporary comparison I wish to make with Forza Horizon (1) is Midnight Club: Los Angeles because they're both open-world racers with different philosophies. Midnight Club's essence is illegal street racing. Forza Horizon, meanwhile, has organized point-to-point races. I guess calling Horizon 1 an "open-world" racer is a stretch since you could only drive on roads.
If you want to be adventurous, play Horizon. If you want to be rebellious, play Midnight Club: LA. I do not want to say one is better than the other since they go in different directions. Plus, I do not want to devalue either game based on preference.