i played nfs hot pursuit, and i felt like it was minigames. pick a race, race it and pick a new one. Felt really grindy.
I recently "completed" nfs most wanted, more open worldy.. A great game. If nfs rivals is more like most wanted than hot pursuit, i think you should buy it. Just make sure your pc can run it.
I think i would like Rivals more than i liked Hot Pursuit.
Edit:
A review of nfs rivals -
https://www.youtube.com/watch?v=ZWySQVvDtGY