It's very fun. It's nothing groundbreaking, and it doesn't push the genre forward, but —notably— it isn't trying to. That's fine! NFS Heat is like a diner meal. It's nothing you haven't had before, but still very, very enjoyable. If you want a racing game that is fun to play all around, you can't go wrong with Heat.
NFS Heat is trying to be a good racing game, and a good NFS game first and foremost. And in an era where almost every racing game (aside from codemasters) is some sort of live service that requires you to keep playing forever to get everything it has to offer, Heat is a refreshing change of pace.
I highly recommend it.