Yes, Mysteryville is a bit simplistic, but when you compare several of these games it's easy to see that great interest and complexity can be developed using the same basic HO mechanism.

I checked out the Wintermute engine and it seems it would likely handle the tasks quite well. Since then I read up on some of the games listed on http://www.ambrosine.com/resource.html and found a couple more likely possibilities.

A well designed HO game would include effective use of many aspects of a "adventure/detective" game. It might depend on what the designer has in mind, paying close attention to overall "look and feel" in the graphics, animations, effects, sounds, transitions, and number and quality of numerous puzzles. All of that carefully woven into the games primary subject and theme. I've chosen HO because I like a foundation of a fairly simple activity which can be adapted to any subject matter and level of complexity and sophistication - with a bit of creative effort.

Thanks for all the input!