I've created a "quick fix" for the crash due to "dmsynth.dll" (Windows 8 only?).
All this does is force Direct Music to fail to load. The game then works fine except sound effects are slightly weird - I think perhaps only one effect can play at once.
Step 1: Download and extract bsdiff for Windows from:http://download.pokorra.de/coding/bsdiff_win_exe.zip
Step 2: Download the patch from:http://www.mediafire.com/?iiaba7p68hb73bl
Find the directory that contains your HotlineMiami.exe file. E.g.
Copy bspatch.exe and hotline.patch to this directory.
Open a command prompt in this directory. (Hold shift and right click to get a "Open command window here" option.)
bspatch HotlineMiami.exe HotlineMiamiP.exe hotline.patch
You can now run (double click) HotlineMiamiP.exe
You will get a message that Direct Music failed to load. Click OK and the game will load normally.
Open HotlineMiami.exe with a hex editor. (e.g. http://mh-nexus.de/en/hxd/
Search for hex string: 7420B8F898
Replace with: 9090B8F898
Save and run.