The Humvee is and will always be and amazing vehicle, it's been off-road porn for many people, but they aren't practical for combat ops any more. They will not survive an IED, that's where the new vehicles come in. The personnel portion has a V-shaped armored hull that deflects the blast, the Humvee's flat bottom just took the full force and then transferred it to the occupants. They tried modifying the Humvees to make them more IED resistant, the last I saw was a chimney type thing. It went from the bottom and through the roof, it was supposed to allow the blast to go through it instead of directly into the cab. I've never seen it on an actual military Humvee though, only online and a few years ago.
The first MRAPs were built to be used in Iraq, a country with somewhat decent roads and terrain that could support their weight and size (almost 38K lbs curb wt). Then we decided to bring them into Afghanistan, which, some of you may know, has completely different terrain. They were getting stuck, hard to maneuver, and if you were really unlucky, the mountain side road you were on would give out and cause your vehicle to roll down the mountain (videos of this are on YouTube).
They then got the M-ATV for use in Afghanistan, much lighter and more maneuverable (27.5K lbs curb wt). It's also designed for a more off-road type use, the lighter weight helps but the 16" of wheel travel also allows it to get over obstacles that the MRAP couldn't.
Now I guess some politicians needed some extra cash, so we get the L-ATV. I haven't driven the M-ATV, so I don't know if they're having issues or not. I do know that we've been in combat and non-combat ops in all different terrain around the world and our vehicles are getting beat up and worn out. I'm sure units who'll actually use them don't mind new vehicles, as long as any input/suggestions that they may have up channeled were at least considered. They have a 14K lbs curb wt, and 20" of wheel travel, I believe they also include a FREE 12 month On-Start subscription (I'm not 100% sure on this though).