* Good Site Design (what is good to me can be a dogs breakfast to someone else. I personally consider the regional heirachy of DMoz to be an almost unintelligible, repetitive maze... to others it may be a good design.)
* Original Content (it was only original when the first author penned it... everything since then is a repackaging of the same basic information)
* Useful Content (useful to who... the site owner, the viewer, the buyer, the seller, the industry, the merchant.)
* Does not replicate anything else on the web (that is a very big ask... in this day and age, anything that is worth adding into a website has almost certainly been included into another site, blog, forum etc...)
In the travel sector, you will usually find each state and region has a big, official govt site. I consider them as authority sites, as I do with much of Wikipedia and Wikitravel. But do they offer unique content that does not replicate anything else? Not even close... they repackage what is, and has been, available on other sites long before they came into existence.
MB.... I'm playing devil's advocate with the bait you have dangled in the water with this post... and for every opinion I have, there will others who totally agree/disagree.
As an industry we have been trotting out "useful content" and "original content" for years as the holy grail for websites. They remain just as much a moveable target now as ever before and will continue to mean different things to different people.
Successful websites (authority if you will) get that way because they fill a market need...and that will probably be because they package their information and services in such a way that it impresses the viewer. The information provided can be found in lots of other places, its just not packaged as well, or used as effectively, as on the authority site.