I went to QuarterWorld this week during an extraordinarily hot day in Portland. Inside they have an original-cabinet Space Invaders. I put in a quarter and started to play. I was certainly familiar with the emulation of this game, but two things stood out as uniquely part of the original experience. Noticing that these qualities could not be represented well, if at all, by emulation, made me think.
The first thing is a shimmery backdrop behind the CRT itself. Some kind of foil it looks like. The second thing is the bass response is great. A unique quality of sound that is hard to recreate.