READ THIS IF YOU'RE A RETURNING PLAYER AND A REAL CAR ENTHUSIAST.
If you own Horizon 4 just keep playing horizon 4. Horizon 5 adds literally nothing new to the table and actually takes away a lot of the fan favourites from horizon 4, most of the British classics from 4 haven't returned. Every Italian brand besides Ferrari is absent. The car pass cars were largely disappointing. They haven't even managed to get licensing for many new 2021+ model cars, so if you were hoping to buy horizon 5 to race newer cars you can forget that. The map is half decent but it's not enough to keep me interested with the lack of quality cars. The whole game feels like it was very lazily hashed together and the lack of new content since launch is just very disappointing. It feels like whomever is making the decisions at playground games on what content to include is clearly not a petrol head or they would have been a little more creative with what models to include under the licensing they did acquire. There are a litany of new cars of all ages they could be added just under the current included brands. Instead they are returning old cars from previous games, as prizes in the seasonal races and pawning them off as 'new content'. This wouldn't necessarily bother me accept most of the returning cars seem to be terrible or boring choices such the 'Sentra V'. Only reason it avoids a 1 star rating is because it does at least look good, the graphics are a slight improvement over 4.
Ultimately it's up to you if it's your first Forza/horizon experience you'll probably really enjoy it. If you're a returning player, you will definitely be disappointed by the cars or lack thereof, also I don't think the map is as good as 4 or 3. It's bigger but emptier.
I can only assume that all the rave reviews surrounding this game must be from first time Forza series players, because the lack of new and interesting content is just baffling. They couldn't even come up with an original idea for the first DLC. Hot wheels was done in horizon 3, how lazy can you get?