Ninjas are mercenaries of feudal Japan. Weve all seen the ninja movies of today that show the many skills employed by ninjas on what are usually, secretive missions. Masters of stealth, ninjas have even been said to know how to achieve invisibility.

The shadow part of the tree is lacking in combat abilities, but not the assassin part.

But that's by design.  The point of shadow is to avoid confrontation and slip by unnoticed.  Or if you do get caught in interlock...escape.

EDIT: I re-read what I posted and asked myself "Well, then why on earth would you want the shadow tree".  And to be honest, I only use it for some select abilities out of it...but a real good use for it is on the hostile server.  If you need to move through an area without getting ganked...Shadow is your friend.

 

Assassin has a lot of attacks...but the way the attacks work, really you stop using a lot of the lower ones as you get higher in level.  Like at level 50 I really so no point to using Punt other than for the coolness factor of the animation.  I mean if you get one shot at hitting an enemy before you have to redisguise/invisi...why waste it on 1000 damage when you can drop 1750 damage with bulldog instead.

 

Some of the lower ones give some status effects, but honestly those are only useful for your teammates.  Assassin attacks don't really require any statuses to execute them.  So, basically you'll probably end up using only Bulldog for major damage, Reverse Bulldog for the stun effect and a little less damage, and maybe Freedom to Joins and Diving Frankenstein as secondary damage abilities when you're waiting for the others to recharge.