Example: in WoW vanilla you (as rogue) could kill fully equipped enemy without weapon ( I don´t mean one shot combos, but rather long CC combos agains which there was no defence). An even if you would use trinket to get out of stun, rogue would just go invis, wait for one of CC skills and repeat (sure macros would help a lot, but rogues were op in vanilla solely thanks to CC and INVISIBILITY).
In Guild Wars 2 right after release rogues would stay far and once you were low health, they would shadowstep you, CCed you with Steal and finish you in 1-2 skills. I literarilly never fought rogue whilefull hp And if i tried, they would just vanish or teleport with a bow. One shot invis guys were annoying as well, demanded zero skill and were relativelly safe to play.
In Fractured everyone except heavy armour guys can go invisible and while we have saves, full offensive rogue might still land most of his abilities successfully. Invisible full offense nuker will be also terryfying. So for me its invisibility combined with cc.
Im wonder what stats for attacks from invisibility will be. Will it multiply any damage (including spell damage)? Will we be able to "backstab" enemy with any (not only assassin) weapon? Will we be able to use any skill from invisibility for damage multiplier ( heavy blow crit from invis would hurt)? Will attacks from invisibility have some kind of aim bonus (as enemy will not be able to tell Im attacking, so he cant defend/dodge/prepare)?
I guess there will be more invisibility abilities, so can they stack (for one superlong sneak to get out of danger easily) ? Is there cooldown on such skills ("you cant enter invisibility x seconds after first invis ended")? Will there be enough skills to counter invisibility (some kind of tracking / marking - i guess perception might help a little, and so will skills from Divination school ... hope they will be castable in full plate, but as they aren´t offensive, they should, right)? Will DOTs show position of enemy (not talking about seeing numbers, but for example blood dripping from enemy)? Will invisible enemy have zero colision? Will we be able to attack "air around" to hit enemy (shift + basic attack)? Will users of low end machines have disadvantage when fighting invisible enemy (in case you would leave footprints on the ground etc. - in original Dota Phantom assassin with her passive would be "invisible" - you could see her only thanks to her shadow (and health bar, but that wasn´t defaultly shown at that time), so if you had shadows off, you wouldnt see her and would just get killed thanks to surprise (and 4x damage multiplier crits :D).
P.S.: Looking forward to see some pvp in upcoming test. Most abilities are still not in game, but wonder how usable such ability will be.