My first thought on reading this is that we can't be that far off from running MAME and every classic arcade game in a browser. Googled it and sure enough - it's already here courtesy of the Internet Archive:
MAME's commitment to accurate emulation is amazing.
Pac Man/Ms. Pac Man comes to mind. Donkey Kong too.
Emulating analog audio circuits accurately requires higher math functions executed millions of times per second. Some of the oldest classics run super slow on sub-3Ghz CPUs.