Illustrator's GPU acceleration breaks Illustrator. Here's how to fix it.

Problems with Illustrator's GPU acceleration are already being well-recorded. In short, it'll smooth things out for you when navigating around your document, but it'll make a lot of your work look bad. If you do a lot of line work, you'll be especially punished.

So look in the top-left corner of the Illustrator window:


Click on the rocketship, then uncheck "GPU Performance":


Now you'll see the rocket ship is sad:


Illustrator will again behave as it did pre-CC2015. That is, art will look right, and Illustrator will sometimes lag.