Prior to the launch of Hotline Miami 2, the system requirements indicated that the game would run under Windows XP. That turned out to be incorrect, which was bad news for gamers who preordered it on the assumption that it would. But that's been fixed now in the form of an unofficial patch that brings the new game to the old OS.
Created by Steam user Silent, the patch requires a certain amount of computer smarts: You'll need to unzip the archive into your Hotline Miami 2 directory, then run the included batch file, which patches the startup file with a custom .DLL making it bootable under XP. Detailed instructions are provided, and honestly, if you're reading this site then the great likelihood is that you won't have any trouble with it.
The instructions recommend that the game be run in OpenGL mode rather than DirectX 9, which can only run in borderless windowed mode and is apparently very crash-prone. The patch will also have to be re-applied every time the game is updated.
Windows XP is pretty grossly outdated by now, but as the Steam Hardware and Software survey indicates, it's holding on to life surprisingly well: It represents only a tiny slice of the OS pie, but it's neck-and-neck with Windows 8 64-bit and has more users than Windows Vista 32 and 64-bit combined. It's too bad that Hotline Miami 2 didn't fare particularly well in our review, but even so props to Silent for making this happen for those that needed it.