Originally posted by Mr Creosote
In general, I wouldn't add any 'second parts' to the list, because they obviously can't be the really groundbreaking ones. 75% of Speedball 2 for example is just Speedball "1"! That also goes for 'informal' follow-ups like Quake (covered by Doom or Wolfenstein 3D) or Master of Magic (mixture of Civilization and Master of Orion).
I'm not so sure I agree with this. For example, Super Mario Brothers radically changed the way the world looked at gaming (for the first time since the great video game crash), and easily eclipsed its source (Mario Brothers). James Pond 2: Codename Robocod had far more influence over its niche than James Pond did (although neither were enough to make any lists). And Speedball 2, regardless of its allusions to the first game, was the one that really mattered and got its claws into the Amiga gaming community, which cannot be said for Speedball itself.
In most cases, though, I would have to agree with you. But I think each game has to be examined on its own historical significance and performance.