Love the way you can set up a complex forum within minutes. Love the way the backend assists you with a clever and deeply logical structure. Did I mention yet that I love the interface? Good. Because I love the interface. Having dealt with other forum software before and having tried not to get too overly mad about them (and not the good kind, more like the "mad hatter" kind), this is like coming to a soothing spa where they play this sweet music and bring you your favorite drink even before you asked for it. And then you wonder whether they will ever stop massaging your feet.
Ninjaboard blows every single other Joomla Forum software out of the water without even breaking a sweat. When I got my hands on one of the first betas, I immediately regretted ever having set up another forum software. (To my defense: Ninjaboard wasn't around then.) My move over the years, through SMF, Joomlaboard, then Fireboard, then phpBB is finally over - Ninjaboard is here to stay.
To some of the other reviews: Yes it needs mysqli. Yes it requires you to install the nooku framework. But you know what you get for that? A formidable extension that is fit for the future years. If you don't like that, then Ninjaboard cannot make you happy.
As for the somewhat lacking documentation: I didn't even check for documentation. Everything just works precisely how you would expect it to work. And give the guys a break - it's still beta software and for that, it is simply STUNNING.