I’m only @OP1 with my melee Zer0, but maybe it helps a bit.
My Spec: http://bl2skills.com/assassin.html#505001000055055105015105515151
Equipment you should get is mostly listed in the Top Gear Thread, I’ll go into the most important stuff any ways.
Grog Nozzle - Ruby won’t quite cut it any more on OP levels to Healthgate properly. Bladed if possible.
Rapier - Slag if possible, but it doesn’t matter much, you won’t fire the Gun often.
2 Slots Situational, I usually have #4 reserved for a FFYL Launcher and #3 for whatever the Situation calls. I.E. Hornet for Surveyor Bots
Shields are Hide of Terra and Love Thumper. LT is easier to handle and the best to get a feel for melee playstyle, as you at least don’t have to pay constant attention to managing your shield. However, the HoT packs a lot more punch with proper parts and the spike as well as the nova are quite useful. You’ll also won’t kill teammates, which the Thumper will do.
Nades are best as a Shield stripper, Storm Front or Chain Lightning will do a superb Job here. To Clarify: It is to strip your own Shield, as the Roidbonus will only apply when your shields are down.
As Relic use a Bone, Element whatever suits you best, although I’d recommend Corrosive/Fire, either as the situation calls for, or if you don’t want to lug surplus equipment around with you probably corrosive (Buzzards, Surveyors etc).
Class Mods Leg. Hunter is easier to use for general mobbing thanks to the big CD Bonus and the 10% heal. Ninja for the big baddies.
Playstyle is to get fairly close, go into Decepti0n, throw out Kunai, strip your shield if it isn’t down already, down your Kunai’d target (you’ll recover your Kunai that way!) throw Kunai, kill, Kunai, kill etc. until you run out of enemies, or make a mistake to break Decepti0n. Switch weapons (Rapier/Grog) as needed while in Decepti0n, if you get thrown out the Grog/Ruby is mandatory to keep you alive. This is also where Be Like Water shines, shoot, slice, shoot, slice rhythm to keep your target slagged will keep the buff up.
Other Differences in the Build:
While Ir0n Hand and Resurgence aren’t bad, they aren’t that great either, which is why I only invested a point each, to get the respective bonus applied from L. Hunter and L. Ninja.
BLW is more useful to me, as I adopted said rhythm (shoot, slice, repeat) when out of Decepti0n which constantly keeps the buff up and as I’m usually constantly on the move LTW is up most of the time as well, which is equal to a 5 Point Ir0n Hand investment in terms of DMG. The HP boost from Ir0n Hand is not really useful. It won’t save you and it can make gating a bit harder to get done.