i don't know what it does definitively but i know it adds a bunch of weird garbage changes like making the menu weird, breaking some cutscene audio and overall isn't very faithful to the original game's look.. or the e3 one. it's just a kitbash of a bunch of random mods and i don't get why it's marked as an "essential improvements"
Topic on Talk:Watch Dogs
I reverted it back to the original mod: https://www.pcgamingwiki.com/w/index.php?title=Watch_Dogs&type=revision&diff=1488343&oldid=1488330