Patch 1.07 for Horizon Zero Dawn is live, and it's focused on graphical issues. Previously there was an unskippable shader optimization at first launch, which this patch replaces with pre-optimization that begins in the main menu and dynamic optimizing that continues in-game. The pre-optimization step can be skipped if you want to jump right in, though it'll decrease loading times if you let it finish. The other big fix: "Anisotropic Filtering now works correctly".
Our review noted that at launch Horizon Zero Dawn was "a slightly inconsistent PC port", running well on some rigs and poorly on others regardless of their specs. Since then, subsequent patches have improved performance and fixed notable bugs, like the one that kept protagonist Aloy trapped as a child forever, and the one that prevented her from walking in the direction the camera was facing, and the one that stopped her hair from displaying correctly when the game was running at over 30fps.
The remaining known issues Guerrilla Games list include instability related to CPUs with over 16 cores, and problems with certain graphical settings like HDR not working correctly, which will be the subject of future patches.