Seeing as stealth tends to get disrupted even by farting, you'd most probably pop out of stealth at the start of casting, and till you'd cast it you'd be hit by a few attacks.

I've tried 2h assassin as NB myself, it didn't work well (at least with light armor - I thought it might be wiser to get more magicka for skills like Ambush and Surprise Attack and Shadowy Disguise, but it turned out I was lacking damage and survival and was pounded pretty darn hard)

Playing NB as melee is really dangerous in VR since you'll be taking A LOT of damage thanks to no class CC - you'll have to level up Volcanic Rune and that drains magicka so sorely needed for Shadowy Disguise.

I've switched to my Angry Mosquito build (forums.elderscrollsonline.com/discussion/90799/working-nb-builds-in-vr)

@‌n0x

Lol you sound just like me. I've respecced my NB countless times already, trying to find a groove that I like. Getting all those skyshards really F'ed me in the A on this...

I actually just respecced to the heavy / 2h build. From stealth for me (Khajiit) uppercut hits for like 2k, while surprise attack hits for around 1.7k.

2h honestly feels like it's the best way to go with this class. You can even make a decent aoe build without swapping many skills. I'll give my builds so folks can try em out.

Single target burst:
Bar 1 - Wrecking blow, Critical rush, Executioner, Ambush, Shadowy disguise. Ult- Flawless Dawnbreaker

Bar 2 - Reapers mark, Rally, Focused attacks, last two slots can be whatever...

You're gonna Mark your target, then buff weapon damage with Rally and stamina regen with Focused Attacks.

Ambush from stealth, Shadowy disguise, Wrecking blow(100% crit from SD and increased by 30% from Ambush), back up a little while target is stunned, then Critical rush( auto crit, dmg increased by 40 from WB and bonus dmg based on distance travelled), Executioner to end it.

Aoe build is simple and mainly relies on building your ult as fast as possible.

Carve, Power extraction, Refreshing path, Rally, Siphoning attacks. Ult - Veil of blades.

Pop Rally, throw down RP, burn magicka with PE, then spam Carve. Ult when it's up. Siphoning attacks should obviously be turned on to proc the 15% magicka / stamina refills, while Rally and PE help to offset the -24% to damage. Carve gives ult for each enemy hit and PE gives ult because of the transfer passive.

While you're not gonna come out unscathed, I've taken out grps of 5-6 VR 2 mobs with this rotation.

I thought about going 2h/5med, but the juggernaut passive from heavy goes really well with this build. 1% weapon damage for each piece. With Flawless dawn you'll be at +17%. Rally's initial boost will soft cap you and it's ticks don't seem to suffer from diminishing returns.

5 med would give 15% crit, but I already get 100% from Shadowy and Critical rush always crits.

For aoe it's just about surviving to get VoB off.

I built it with pvp in mind , but I honestly avoid the mess that Cyrodill is right now.
Thing to remember though is that Ambush only stuns on pve. In pvp it's an immobilize, so you'd have to be quick with the Shadowy / Wrecking blow combo. Even then a smart player will block during the immobilize saving them from the knockdown.