I've been playing Rivals all afternoon. There's a very simple litmus test to determine whether you will like it or not.
Did you like Forza Horizon? Y/N
...because it's basically that, in 1080p, with cops.
In other words it's fucking awesome. :-D
How is it compared to most wanted? I never really liked most wanted because of how cars handled and how easy it was to get that crash cut scene. But I have watched a lot of Rivals streams, and it looks really fun. The map looks a lot more fun than Most Wanteds map