First of all, this pack is best for loads between 10 and 25 pounds. Less than 10 pounds and I'm on a day hike where the G4 has too much volume. More than 25 pounds (rock climbing gear) and the suspension can't handle the weight.
It seems very durable if you treat it with care. I seam sealed the pack thinking this would help reinforce the seams (and make it a bit more rainproof). I've torn one small hole in the mesh pocket, but that was when it was stabbed by a tree while bushwacking. Not the pack's fault at all. K-tape fixed the hole just fine.
Some might want a sternum strap. This could be easily done with a bit of velcro attaching to the shoulder strap padding pockets. If you look, you will see what I mean. Tall people won't be able to do this because the pockets will be too high up on the shoulders. After writing this I did create a sternum strap by girth hitching a buckle to the thumb loops. Worked quite well.
I'd like the pack to be taller and narrower, but that is because I'm a tall and narrow guy. I think it would make bushwacking easier for anyone.
The pack is well designed and well made. The mesh pockets are very big, but not too big. The roll top closure is effective and looks cool. I removed the bungee drawstring from the top of the pack since the roll top works so well (and I never fill the extension collar).
When I first got the pack I thought it would be worth an ounce or two to add compression straps to stabilize the load and pull it in to my lumbar region. After using the pack I no longer think they are necessary, though others might want them.
I use an eight section z-rest as a frame. When I first started cramming it into the pocket it felt very tight (like I should have been using the six section z-rest the pack was designed for), but now it fits just fine. Either the mesh has stretched a bit or I've become used to the cramming. The z-rest can be placed in the pocket so that it folds towards your body, or away from your body. Support is much better if you let it fold away from your body. Since I need more padding when I sleep, I carry an MEC bivy pad (5mm x 50cm x 150cm, 6.5oz) to supplement the z-rest. The bivy pad fits inside the G4 and adds padding and structure to the pack.