Space Invaders (Arcade)

As can be seen from these frames from this video and this video, Space Invaders has a vertically oriented monitor which makes scan lines appear vertically, not horizontally. .

The CRT display is mounted facing upwards, reflected towards a semi-transparent mirror, behind which is a plastic cutout of the planetary surface. The reflection of the CRT appears over the cutout, serving as a backdrop. The CRT had colored overlays on the display itself, to add color to the black and white image. Thus, both the colors and background of Space Invaders are non-digital optical effects. Also note that the actual CRT image is mirrored to appear correct in the reflection.
(Photo by dbrainjr on ebay.com)

I adore the little animations where the invader steals and flips the Y in PLAY, and the red invader shooting the extra C in INSERT COIN.

I played with the MiSTer backdrop enabled. I still think it looks weird, but the game looked more or less like this originally.

For a while now, I've been using a custom MiSTer video filter with interpolation and subtle horizontal scanlines. Everything looks great, but I realized that arcade games with vertical monitor orientation should have vertical scanlines, not horizontal ones. I never really looked for this, but confirmed it with YouTube videos of the real arcade hardware. I have now made a corresponding vertical video filter for games like Space Invaders.