Nightblades currently are in a bad position,
we've experienced it ourselves, and we've seen the topics rise left and right.
I personally play a Nightblade and experience quite a bit of frustration when Dragonknights and Sorcerers seem to outperform us vastly.

This is not to say that Nightblades cannot function, (I'm VR9 and enjoy myself, I can tank comfortably and a Nightblade healer would never run out of mana) I'm just saying that Dragonknights and Sorcerers have better tools to get the job done.

I believe this is caused by several reasons:
- We are bugged as hell.
This will get fixed, but I do experience and understand the frustration. Certain playstyles cannot work with the bugs in place. (dotting someone up and withdrawing back to stealth, before reopening doesn't work, dealing damage takes you out of stealth, even when it's just a dot)
- Our numbers need tweaking.
Certain abilities are very nicely designed, but the damage and self healing seem to be a bit underwhelming in comparison to other classes.
- We are partially stamina/melee oriented.
Haste focuses on weapon attacks, and stamina recovery
Master assassin increases weapon damage while in stealth
Surprise attack lowers an enemies armor against physical attacks
refreshing shadows, more stamina regeneration

This part of the class pretty much shouts "uuuuuuuse stamina you fool!"
Sadly enough, most stamina oriented abilities deal a lot less damage and healing then the magica alternative.
"But!" you might say "stamina is much more useful, you can roll away from attacks, block damage, interrupt people with it!"
And you are completely right in saying so, which is why it would be so comfortable to run around with no stamina abilities at all present on ones bar, you can better use that resource for stealthing, dodging and running, instead of doing underwhelming damage with it!

- Our survivability is saddening.
Which is not a problem, if our skills were not whispering to us, "Hey, psssst, you can go melee combat, I've got some very nice close combat skills for you"


So, from the looks of it, the ultimate Nightblade runs around in light armor for mana recovery, a resto staff strapped to his or her back to assure some healing, and in the other hand a bow! And I truly believe such a Nightblade would work very well, and might even be on par with other classes.
Though if you're sporting that style, a sorcerer would do it better.. *sadface*

So, is it all doom and gloom for the Nightblades?
Currently, yes. It's a tough life.

So, how do we fix it?

Currently Nightblade fixes are already happening, together with buffs planned.
Personally I believe that if the Thieves guild and Dark Brotherhood are released well gain some very nice abilities with good synergy towards our class, especially if these are decent stamina oriented abilities.

Things can only get better from here on out.

So I recommend we practice patience, or sorcery till better times arrive.