Thanks for that link.
As I read through this, its... really, really good. As in, really well written.
Two bonus damage features. One from guild training, which grants +cha damage when you hit an enemy who has no other enemies adjacent to it. So you want to take creatures off alone and beat them like an avenger. But the assassin's shroud ability is the big one- it grants a significant amount of bonus damage based on how long you spend studying the target before deciding to take advantage of the fruits of your study. For this paragon character, you can get up to +4d6+12, rerolling 1s on the d6s, with +3d6+9 if you miss.
Meanwhile, what makes this really, really nice, is how it synergizes with your other abilities. The Shadow Storm at will lets you deal extra damage based on how many creatures are adjacent to the foe you attack. The theme is that their shadows are tearing at your enemy as your sword does as well. That encourages enemies to accept isolation, or to at least put them in a bind about whether they want to take +cha damage for being alone, or +X damage for having creatures adjacent. You can study creatures other than the one you're attacking, and you have an at will that lets you teleport short distances as long as you end adjacent to a creature- the theme being that you're jumping from shadow to shadow.
This means that you might spend a fight beating up on a lone creature while carefully studying the big, bad enemy that's the real challenge- then after a few rounds, teleporting away from your current target, popping out of the shadow of your chosen victim, and stabbing them for some really ridiculous amounts of damage.
The whole thing just seems very flavorful and very well done. I really approve. Flavorful characters who use magic in a well themed manner instead of the generic elemental grab bag of traditional D&D magic are usually my most favored characters in the game. I think this guy's going to give the Avenger a run for its money in terms of popularity.
There are a number of other tidbits, but you can probably browse on your own for them from the given link. Remember to enlarge the images if you can't read. Choose "original" size.
My only gripe is all the great art depicting Assassins with katanas. The game doesn't have a katana. The example assassin has a bastard sword (its a halfling, so probably that's the best two handed heavy blade for him). The game really SHOULD have a katana, and no, retheming a bastard sword in a game that already gives props to such an incredibly large list of weapons, up to and including obscure egyptian swords, isn't enough.