[aderack]

I suppose it depends on how you define "investigation". Metroid is a hell of an investigation game, for instance. Exploration is facilitated by investigation, and exploration is the big point. So.

Shenmue is pretty much built around investigation -- albeit investigation with absolutely no mechanical significance.

I know you're referring to games outside the point-and-click universe; still, Riven.

What investigation demands, really, is for the small to take precedence over the grand. The player has a vast number of options, and must filter out the noise to find a few things of significance, then determine the nature of that significance. This is a difficult model to implement, as it's inherently inefficient: the developer has to create reams of "junk" information in order to provide context for a relatively few points -- and then it must somehow draw the player's attention to the small and specific, in the face of the vast and general.

Though a neat model in theory, it is pretty hard to justify unless you really know what you're doing with it.