Since TG patch, in which the most scary and bad designed feature was implemented (animation prioritization) not only fights became much slower because although most of skills are of instant cast most of them have unnecessary long animations.
However, prior to it, the Ambush skill could be blocked as long as you were able to see the enemy doing the characteristic movement and you started blocking. But now it seems that most of the times this skill can't be blocked because its animation is super short and seems to be triggered much earlier than the blocking animation (speaking in milliseconds, of course).
The results are terrifying, both in PvP and in PvE as well. In PvE, mostly in dolmens and places full of Nighblades, like veteran Fungal Grotto, the only way to not be stunned by this skill is walking towards the enemy holding block. In dolmens it's slightly worse because sometimes behind the Nightblades there are casters abusing of unblockable Fear. For stamina players is not a big deal, but for the rest, if we want to avoid the Nightblades we won't have enough stamina for the following break-free.
As of PvP, it promotes the abuse of the skill. Today I was running dolmens in Cyrodiil today, very casually, and two Nightblades went out of stealth right after finishing the boss and one of them spammed 6 Ambushes in a matter of seconds. I couldn't react because my shields are slow, my meteor is slow, my active bar can't afford hold buffs because Molag Kena's animation lags when changing bars (so I can't let shields and Liquid Lightning in the back bar, for example) and in the end those retardeds got the whole XP (closing the pinion) and the chest I did all the work for because of this futile feature added as workaround for the biggest issue in fights (animation cancelling)
I am the very model of a scientist Salarian, I've studied species Turian, Asari, and Batarian.
I'm quite good at genetics (as a subset of biology) because I am an expert (which I know is a tautology).
My xenoscience studies range from urban to agrarian, I am the very model of a Scientist Salarian.