The article "Interesting Tricks" did of course not exclusively apply to juggling. It applies to tricks of any kind.
Read the article linked above to catch up on my definitions of: Impressive, Visually appealing, Conceptually interesting, Novelty or Surprise, Recognition.
What makes juggling tricks special, what are its strengths?
In juggling there seem to be more possibilities than in for example acrobatics. Therefore there are a lot of opportunities to innovate and surprise your audience with novelty.
Also, a repeating pattern can be set in a matter of seconds. Even those who have never seen juggling before can be conditioned quickly, so you can break their expectations.
Juggling tricks are often easy enough to perform them in many different ways. Therefor we can even put other actions (thus recognition) in our tricks. For example eating apples, clawing the balls like a cat or kissing them like a stereotypical Frenchman, tricks which street performers commonly use. Of course the out of place recognition of these actions also surprises your audience.
It remains easy to dance or move in certain ways and juggling tricks can easily be used as metaphors.
With a large group of jugglers having seen thousands of tricks, it is possible to create tricks that are conceptually interesting simply for the sake of the trick. What can we do when we combine a ring and a club into one single prop, and create a club with a hole? These are the kind of questions that team RDL asked for example. Concepts like for example: Balances, bounces, rotations, siteswaps, pirouttes, isolations, prop combinations etc are explored to extreme depths by various jugglers creating all new sorts of ideas. With infinite possibilities juggling allows for easy and fun experimentation.
Juggling can be very aesthetic and visually appealing. It is often rhythmically pleasing, and the performer can easily choose and change what props, size and color he wants for his display. It is similar to dance in that it is about movement, but not necessarily with the body. Trick mastery allows for the search of the most aesthetic variation.
As long as props are out of our control there is a certain tension about if we get them back. With multiple props it is not hard to make tricks look very complex. Seeming to master this complex risky pattern is impressive. So impressive that audiences often have unrealistic memories about jugglers, exaggerating the number of balls they have seen.
Juggling has way more strengths than this, I am sure of it. You are welcome to list your favorite in the comments.