Motion blur is great when done right, but most games do it wrong, so it gets a bad rap.
The two sins are:
1. Blurring things that shouldn't be blurred.
2. Blurring too much.
Racing games are notoriously guilty of #1. If you're in a third person view, your car should basically never have any motion blur. Likewise, a car driving the same speed as you right next to you shouldn't get blurred. You should only see blur in the road and scenery that is close to you. Instead, the devs will just apply a post-processed radial blur that blurs the entire scene, which just turns the entire screen into a blurry mess.
The width of the blur should at most be the delta between frames, and ideally, just half that, really. But a lot of devs seem to have this idea of "Motion blur is a neat effect! We should emphasize it!" and the blur will cover an area covered by multiple video frames.
A motion blur that is more subtle can actually look amazing. It doesn't look blurry, and instead, just makes animations look more fluid.
Motion blur is why movies can be 24 fps and look fine, but a game at 24 fps typically looks incredibly choppy.