You'll be disappointed to hear this. :-(
OS4 doesn't emulate any of the original Amiga's custom hardware, just the CPU. So while you can play some more recent games that were designed for use on graphics cards, you won't be able to just run any old Amiga game from floppy.
Obviously you can run UAE on top of OS4, but that's subject to all the same restrictions as running it on Windows. (You can't directly access floppies, etc.)
