manual, but with an extra block
See Also - sequels, prequels, same universe...,maybe clones/mods
Similar - similar gameplay eg. UT is similar to Q3A, OpenArena, Quake Live, War§ow etc. (all of them are pure tournament shooters, no story, no campaign...)
maybe for Quake IV:
See Also: Quake II, Quake, Quake Wars
Similar: DOOM³, PREY , Duke3D etc.
I picked up that idea and created a block that shows similar games from one category of the game, e.g. shoot them up or platform. The ranking is random, so every time you enter the page you see different games listed there.
In addition to the hand picked similar games it created a more associative selection for the rather random browsing user.