Shadow warrior is great. But you do need to practice with it, you'll mess up a lot early on; timing is crucial as is understanding the exact mechanics of stealth.
Spell Absorption will break shadow warrior. You can't be an atronach AND a shadow warrior.
Companions break sneak attacks. You cannot sneak attack an enemy who is in combat
Melee is all about timing, my favourite strategy is to bash them with a shield and then cloak -> sneak attack them while they are staggered. Keep practicing til you master the timing... also use a dagger, easier to time it and better sneak crit damage. Don't bother trying to use power attacks or dual attacks, they'll just slow you down. better to strike swiftly and reliably, then rarely but strongly
Ranged is all about positioning. The time it takes an arrow to travel and launch is too long for shadow warrior to directly help with. Instead, you must mis-direct an opponent; find a pool of shadow, cloak just before you enter it, and somersault to another position lateral to where you entered. The enemy will search for you where you entered, but they will no longer know exactly WHERE you are (searching Vs aware) - An enemy who cannot see you, is open to sneak attacks.
before long you'll be like this guy
http://www.youtube.com/watch?v=KETNiqHg0oM