Don't listen to what anyone else has said. Sneaking DOES make you completely invisible if you put Perks into it. You can walk right past enemies and they will not notice you. It is the equivalent of perma-Chameleon in Oblivion. Couple that with the fact that skills synergize so well with Sneak and you get crazy multipliers that kill most enemies in a single hit. Considering how encounters occur also, Sneak becomes infinitely more powerful. Enemies almost always have their backs to you in a room line of sight of a doorway, or are standing still right out in the open with giant "free kill" signs over their heads. It isn't often you encounter more than 2 enemies at a time, and even two enemies at a time is pretty scarce. By the time the second enemy even realizes their buddy is dead, you can usually get the drop on them. This is especially true if you are ranged.
If you get the Muffle Enchant or double up Sneak Enchants you will be permanently invisible with perks. It does take a lot of fun and strategy out of the game as you can ALWAYS get the drop on enemies. Rarely will you ever run into a situation that due to multiple targets the enemies will spot you after you killed 1 or 2 targets. If this happens, you just derp it up and sprint away using Shadow Warrior and eventually will pop back into Stealth.
So is Sneaking "overpowered?" Heck yes it is. Sneaking trivializes the game and if anyone else tells you otherwise they are morons...but it can be fun being overpowered.
/That is all.
Do not understand, have over 90 in sneak, yes you can always get the sneak attack with bows, and melee if not in daylight and in front, however once you hit they start searching, if less than 5 meters away they will find you.
Undead are more unaware but not so much as in Oblivion where you could stand and shoot at them until they died at three meter range.
Main benefit in Skyrim is that base damage on weapons is higher so the enemies goes down faster, this enables you to shoot down multiple enemies before they finds you.
Has not taken the master perk who enables you do get into stealth again if discovered, if it blanks everybody memory of you it's overpowered.