While I honestly find the DPS aspect of GNB's toolkit to be pretty awesome, I have some reservations about GNB's defensive utility, especially when compared to the other three tanks. While GNB is privy to the most defensive mitigation CDs with Camouflage and Heart of Stone, I often feel like I'm dead in the water when any of my defensive CDs are not up. I'm not necessarily opposed to the idea of this being GNB's unique defensive playstyle, but I believe there should be a few tweaks to some of these tooltips to make it so I feel like less of a burden on my healers.
Camouflage
I'm not sure if an increased parry rate would help much here; I know many would just do away with the parry rate entirely for something more generally useful. However the 10% mitigation for twenty seconds every 90 seconds isn't terrible. As of right now I find myself using after my first use of HoS as I can ride that twenty second buff until my second HoS is up. I feel like maybe just a reduced CD would make the ability somewhat more attractive. At the least I don't think it should share the same CD as Rampart, as it definitely feels inferior to rampart.
Heart of Stone/Brutal Shell
Simply put I feel as though Heart of Stone should be increased from a 7 second buff to a 10 second buff. Its 25 second CD is 10 seconds longer than The Blackest Night and definitely less useful, especially with regard to tank busters on boss encounters. Paladin's sheltron is also better in that it's more readily available and by level 80 is a six second block buff -- and is a part of a defensive toolkit vastly superior to Gunbreaker's. The 15% buff is still welcome all the same, and also promises good OT utility in that it can be applied to anyone in the party.
However I find the added effect of applying brutal shell onto a secondary target to be one of the least exciting aspects to any tooltip in this game. Brutal shell itself is not exciting. I understand its parity with Souleater or Riot Blade or Storm's Path, but it simply does not make a meaningful difference in combat. Certainly I could never see myself going out of my way to apply HoS onto a party member in order for them to get a shield that's worth approximately 3% of my total health.
That being said I'm not sure what to do with brutal shell. My only idea is that the effect could be applied through some other skill/skills so that shielding as a GNB is an active party of your defensive rotation.