The problem with this is that the assassin partly relies on large weapons for their damage since shrouds are slow to stack and often either get wasted by a miss, overkill or from other PC's who are focus-firing the mob and kill it before you can invoke your shrouds.
I'd try a rogue for the build you want and use Distant Advantage in combination with Fleeting Ghost. You could perhaps multi into assassin for some invisibility powers but I think you'll find that a ranged dagger rogue works quite well using the standard stealth/cover rules and Deft Strike.
I'm not sure I understand the 'problem' with assassins. Warlock's Curse, Sneak Attack etc are also often wasted on a miss as you often don't get more than 1 attack around anyway, so the assassin is already somewhat different in that he can apply damage from his shroud even if he misses. Overkill isn't any different to other strikers either. Your target dying before you can apply shrouds can be an issue, but with decent planning shouldn't happen too often. So really the 'problem' with assassins is that they can use bigger weapons? Ok...
That being said I do think they top out on damage lower than rogues/rangers & barbarians, but I still think they look like a pretty decent class.