I agree that some sort of rating system might be nice. Right now for a lot of worlds the only way to judge anything about it is to download it. Until I download all I'm being sold on is the picture and the description... It isn't until I download I can see what the system prompt is like, how many entities there are, stats, how many locations, how many dictionary entries if any, whether or not the traits make use of author-provided javascript that scares the heck out of me from a security perspective...
So I find that often the download count gets inflated purely because the description / picture was enough to intrigue someone... But not necessarily make them play it.