4 years now on my 2010 model. 61K miles. No problems. I've done nothing to it except oil and lube, tires, and brakes, and other normal maintenance activities.
I've had it in some situations I shouldn't have been in...pushed so much mud with my front bumper once that I tore my front license plate off (never did find it), but it kept on going. I frequently take it to my brother-in-law's camp. The road to camp is a creek that you have to drive in at points. Never had an issue and almost never have to use 4WD. Plenty of room to carry supplies with the back seat folded down.
It doesn't caress you in luxurious isolation to the point that you feel as if you aren't involved in the driving experience, but it isn't so tiring that you can't take long trips in it. It's not luxury car smooth, but coming from a JK, it'll be just fine (I had a TJ Wrangler before I got my Xterra and it was like upgrading from a Camry to a Lexus). The IFS makes it ride and drive much better than a Jeep with two solid axles.
Mine averages +/- 18 mpg or thereabouts. 265 horsepower 4 liter V6, 281 lb ft of torque, with a curb weight of just a tad over 4000 lbs. Reluctant to downshift (gotta game that EPA cycle!), but once you put your foot down, it moves out pretty quick. I've pulled at least a couple of vehicles out of trouble that were bigger than mine and power was never an issue.
It is built on the same platform as the Nissan Titan/Frontier and has a fully boxed frame for strength.
There was a problem with the radiator/trans cooler mixing things up on the 2008 and earlier models, but it seems to be mostly sorted out after that. Nissan extended the warranty on the radiator/trans problem out to 80,000 miles for 100% of replacement coverage, and partial coverage to 100K miles. I'm not that worried about it myself, as very few 2010's have had issues.
Very happy with my Xterra and would buy another one again.