As a defense contractor who repairs Humvees, I can tell you that they are good at a lot of things and operate well in various environments. The major problems you encounter in one are from the geared hubs and the engines. They have been made with several engines since inception and I personally don't like any of them. The oldest ones were prone to cracked blocks and all are underpowered. The central inflation system makes it feel like you are riding in a rock tumbler. I fit weren't for the military's extensive collection of parts and their maintenance capabilities, I think the Humvee would have fallen by the wayside. Just the mere fact that you can only get 4 people in that goliath of a vehicle is absurd. I think if they added some protection for the geared hubs and converted the engines to a Duramax or Powerstroke then they would have something.
A friend of mine who is notorious for showing off how much money he has, has got an H1 that is decked out. In the past year, he has drowned it in a creek, burned up the winch, had a cracked block, cracked transfer case, and busted radiator. Only the drowning was done on the trails. The rest happened on the street. It's definitley a poser mobile with the thousand pounds of racks and brushguards he has, twin DVD's, GPS, sound system, KC lights, etc...
The only good upgrade was the 38" TSL-SX's. BTW everytime we go on a big ride he jumps in with one of us.