I played for 7.5 hours and here is an early review:

+ Cars handle way better than FH4, you can really feel when your tires hit the ground.
+ Mexico is a great open world. I really liked the design of it.
+ Graphics are just... damn (but pc port is kinda sucks, wait for cons). It is one of the best looking game i have ever played
+ Story mode is very satisfying to play, cutscenes and dialogues are way better than FH4, and our character can talk now!
+ Variety is enough
+ New rewarding system is way better than FH4, i find myself doing races (i don't like racing in racing game lol - i'm happy with colletibles and crazier events) because game actually rewards you well.

- PC port is bad at the moment. Textures look really low quality even in ultra and extreme. Also lots of crashes and bugs. They'll be fixed -im sure- but still, not a perfect day one experience.
- Some UI elements are just copy paste from FH4 and i don't like it. I want feel like i'm playing a different game.
- Photo Mode is not enough -for me-

I will update this review when i play more after my midterms, cya