Its not just hype they are fun.
I bought an On One Fatty at the start of the year and loved it to bits, and then along came a Moonlander and now a Krampus. Its a very different type of ride you get from them, totally big kid giggling, but dont think that they smooth trails out a make riding easy by any means, yes they are specifically for soft ground conditions but the steeper head angle and short chainstays on the Fatty make it a hoot on any trail centre terrain that isnt rocky to the degree where our getting bounced around everywhere by the uncontrolled tyre damping (like GT red/blue)
The moonlander is an absolute barrel of laughs, fitted with 4.7 Bud and Lou tyres its a monster, and leaves a smile on your face for so long after a ride people will think your mad.
The Krampus, as you know is a different beast, but a true surly beast nonetheless, very fun on 'trails', I did a 50 odd km ride on mine yesterday, lots of different terrain, from off piste singletrack to fireroads, mud, bogs, swampy rock fest a boggy rockfests, the krampus lapped it all up and left a big smile on my face which is still there now as my legs ache like hell
Don't be sceptical but dont jump on the bandwagon straight away, try one first, fat biking on the beach is still mtbing but its a special way and place to ride, or try a Krampus on some natural trails, horses for courses, not just a fat tyred bike for everything.