Well, mostly box-shaped houses are good because they work well, so why run yourself down? The wierd and extravagant designs which look so wonderful often are extremely difficult to play, with sims getting stuck in corners etc! I tend to go for fairly simple shapes and open-plan kitchen/dining areas with lots of room for sims to manouevre around each other! And since most of my houses are in a half finished state when I tidy them up, they are still fairly adaptable.
So true I have found this with a few I have downloaded.Tthey looks so beautiful but in play mode I have had to either redesign them or get rid of them because they are unplayable as they are.