EDIT: Get the final update,
check this post ------------------------------------------------------------
NEW UPDATE!!! 104 Campaigns, 268 Single levels!
And this time, something extra: custom music is already included in the zip file (for those campaigns that do have a custom soundtrack, like Real Human Bean 2)
How do you install a custom music mod? Get the hlm2_music_desktop.wad file from the campaign's "music" folder, then copy it to your base Hotline Miami 2 folder (I suggest you previously rename the original file so it doesn't get overwritten, that way you can go back to the game's awesome soundtrack any time you like). This takes just a couple minutes and it's really worth it to appreciate campaigns the way their author intended.
Just get this big file (5 GB), everything is in it:
link outdated, see next post Uncompress the zip file to /My Documents/My Games/HotlineMiami2/ keeping folder structure, so that the /Levels/campaigns and /Levels/single folders are created right there. Then, launch the game, go to Editor, and you should see at first the single levels, hit Escape and move left to select campaigns.
As always, huge thanks and respect to every mod and level author whose talented work is included in this compilation.
Enjoy!