Assassin PvE mainly just received quality of life things: easier ways to stack poison, easier ways to stealth, all CCs without sacrificing anything, proper elemental damage AoEs (before it was an element we couldn't raise), Awakened Heart Stab, etc. Their overall playstyle didn't change too drastically. With gear though, a few key inputs change that make it either a party burst or solo sustained build.

Assassin PvP was significantly buffed, now sitting on the top two spots alongside Warlock. They have increased ranged on a good number of CCs, two of which are now gap-closers, their ability to stack poison is overall easier, and one of their iframes were improved. Lightning's tools of overall easier stealth are pretty busted in the PvP setting.
However, they did receive several noteworthy nerfs. A good chunk of our CC options were removed (one Unconscious, one Daze, and two Knockdowns), one of the aforementioned CC gap-closer can be approach disabled, and another CC gap-closer, despite gaining a defense penetration, has a significantly shorter queue duration enough for it to be predicted (originally we could just run to the other side of the map and wait for you to drop your guard before we can use it) or us to be stun-locked long enough for it to time out. Last but not least, their infamous stealth evasion, Webbing, Turning Leaf, and Ice Mine were all toned down, and they can no longer use their defense break skill on ground counters.