One of the most important precedents in videogame intellectual property litigation is Atari, Inc. vs. Amusement World, Inc., a 1981 case that involved a game called Meteors by the defendant, which Atari claimed infringed on the copyright of its popular game Asteroids. Atari sought an injunction against Amusement World and its president, Stephen Holniker.
You can read the entire decision linked above, but the court decided that Asteroids and Meteors were not substantially similar due to the fact that the two games represent different interpretations of the idea of a game "in which the player combats space rocks and spaceships."
While the decision acknowledges a number of similarities between the games, it also notes a number of differences. For example, Meteors was in color, had shading and a background, and had a ship that fired continuously. With respect to the similarities, the court notes that these "were inevitable, given the requirements of the idea of a game involving a spaceship combatting space rocks and given the technical demands of the medium of a video game." Naturally, the technical demands of the medium were quite a bit different in 1980 than they are today.
From the perspective of video game history, Meteors may not offer very much interest. But from the perspective of IP litigation, it's an important example, because it offers an early, concrete decision on the idea/expression dichotomy in games.
The problem is, Amusement World wasn't really a going concern as a cabinet manufacturer even before the expense and trouble of Atari's lawsuit, and Meteors was never widely released. It's been very hard to find any documentation of the game, save for the 1981 decision, which just describes it.
One could speculate, of course, on why the court would have decided that the two games were not substantially similar: it's always been clear that Asteroids was a vector game and couldn't have been made in color with that technology. Based on the court records, it's reasonable to conclude that Meteors was made with a raster display, and that the changes described in the decision would indeed likely have made it not substantially similar to Asteroids, at least in its audiovisual appearance.
But it seems we won't have to speculate any longer. Just recently, Stephen Holniker's son unearthed one of the game cabinets and installed it in an arcade/LAN center he runs. So, for the first time in a long time, ever maybe, we finally have some documentation of Meteors and what it looks like (skip to 2:00 for gameplay footage).
As you can see, the results confirm the relatively easy guesswork I laid out above: it's a raster graphics game with bitmapped ship and rocks, overlaid upon a stellar backdrop. Visually, it looks a bit like Galaga or other space shooters of this era. And while the game certainly derives from the same concept as Asteroids, it doesn't seem to look like it, which is the whole crux of audiovisual copyright cases. Now that visual documentation exists to exemplify the 1981 court decision, I suspect we'll see this example come up far more often in such contexts.
Disclaimer: I am not a lawyer, and this is not legal advice.