I absolutely LOVE LOVE LOVE my truck. I wouldn't want any other engine in my truck besides the 6.0. It's awesome. It is the last real diesel in my opinion. It sounds like a traditional diesel. The newer trucks are all quiet and have even more emissions related crap than the 6.0.
Most of the problems with the 6.0 engine are related to government mandated emissions equipment. There are many common problems with the 6.0, but if it is kept stock without tuning, it is very reliable. The rest of the truck is BUILT FORD TOUGH like always. The interior is amazing, especially the King Ranch. The transmission is awesome. The Dana 60 front axle is super strong, unlike that independent front suspension crap GM is using now.
If you tow a lot of weight all of the time, you could maybe expect some head gasket issues. To keep that from happening you should: Replace head gaskets, mill heads to make sure they're flat, and install ARP head studs in place of the head bolts Ford uses.
An aftermarket coolant filter is also a must to remove the remaining casting sand and particulate in the coolant that will eventually plug the oil cooler, and cause the oil cooler and egr cooler to fail. This is the primary reason why they fail.
Change the oil every 5k and fuel filters ever 15k and you'll have a super reliable truck. I also run 1 oz of 2-cycle outboard oil per 1 gallon of fuel to keep the fuel injector and upper cylinders lubricated with the new ultra-low sulfur diesel fuel.