This is pretty much the first excursion my husband and I did in Jordan, and I definitely recommend seeing it sooner rather than later if you're taking a short trip to Jordan. It's definitely no Petra, but it's still pretty amazing.
As an American, even a well-traveled one, I'm still always so amazed that I'm allowed to touch things and don't have to stand behind a rope 20 feet from an exhibit. At the citadel you get to actually climb on top of the ruins.
You also get a great view of the city from this vantage point.
If you're an English speaker, I recommend not getting a tour guide. The informational plaques and info at the on site museum are all thorough and available in English.