Will it?
Will it break FoxFi [probably]? Will it fix the inability of Sense to rotate the home and lock screens [no]? Will it free up more memory to prevent poor task switching [no]? Will it fix the contacts and LTE problems some people have [maybe]? Will it make the settings and other menus sort in alphabetical order [probably not]? Will it introduce any new bugs [possibly]? Will it be the last major OS update the Evo LTE will ever see [maybe]? Will it add USB flash and HID support [I doubt it]? Will it take away USB mass storage mode [might]?
Trust me, there will be plenty to continue to complain about, regardless of the OS version, the handset, or the manufacturer.