I think in some ways fat bikes are more maneuverable than standard mtbs as the tyres have a lot more grip. I find riding my fatty to be much more confidence inspiring going round corners than my not so fat bikes due to the amount of grip available. The amount of grip makes climbing a lot easier too - it just monsters up climbs. As for doing downhill, the one drawback I notice is that the weight makes it slightly harder to tuck the rear end up underneath me when getting airborne, but then the big tyres make landing much more comfortable than a hard tail with skinny tyres.
The go anywhere nature of the bikes makes them ideally suited to a bit of chilled out exploration, or bimbling. Yes, they are not as out-and-out fast as a standard mtb, but they are pretty close if that's what you want to do. But ultimately, the thing that makes them better is that they are fun all of the time.