In terms of interior space, your first consideration after square footage should be ceiling height. It doesn't contribute to the advertised measurements -- unless used as a selling point -- but depending on the year and style of the architecture involved, ceiling height can vary widely, and it has a subtle but great impact on the way we view our home spaces.
In fact, ceiling height is nearly as important as light itself. A high ceiling can collect light and make the space seem far larger than it truly is, while a lower ceiling contributes to that "dungeon" feeling you want to avoid.
However, low ceilings shouldn't necessarily be a deal-breaker. Through placement of art, mirrors and other eye-catching objects -- or clever use of wallpaper or paint -- you can increase the impression of height without feeling cluttered. The walls aren't really closing in, after all!