Patch 1.07 (opens in new tab) for Horizon Zero Dawn (opens in new tab) 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 (opens in new tab) 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 (opens in new tab), and the one that prevented her from walking in the direction the camera was facing (opens in new tab), and the one that stopped her hair from displaying correctly (opens in new tab) 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.