http://www.co-optimus.com/review/1963/p ... eview.html
Interesting article regarding the co-op mode in Forza Horizon 3.
Main points i take out of this (as well as my own playing) is that there are 3 main co-op/online game modes in the game:
Online Adventure = Race against other players (as well as your party) to 4 different events and the person with the most XP at the end of the 4 evens is the winner - you get XP, Money etc no matter where you finish. This can also be done as a private lobby if we just wanted to play with just each other.
Online Freeroam = Assuming this is just driving around the map with your mates and online people, with all events in single player available. You get the option of joining other peoples events if you wish. You can also do this as a private lobby.
Co-op Campaign = Play the full campaign as a group. One person becomes the leader and invites other players to join. They then take part in the activities that the leader selects. The difference here is that any race that the leader selects, becomes a 'Team' race, where the red team (human players) race against the blue team (AI Players) and the team with the most points at the end of the race wins. Its very similar to a 1st vs 8th race but you can finish 6th and still be on the winning team if your team mates finish 1st and 2nd. Very good idea IMO as it means you don't lose heart if your in 6th and 1st is a mile ahead; You focus on gaining as many places as you can so that your team has a better chance of winning. I think you can also jump between playing the campaign by yourself and playing campaign co-operatively. Any race you do goes against your progress.
IMO i'm loving this game, and i really hope the next time it comes on sale you consider picking it up. It does also mean because i'm already playing the game and you both do pick it up, its no problem me jumping in on your campaign's when we game as i just enjoy driving around in different cars anyway.