The Kill moves are nothing but a "Plus" from a player perspective, but from an Enemy (As in, being used on the player) they're irritating. Since they ignore any Evasion the player might have been able to do, they put undue emphasis on powergrinding your defense as quickly as possible.
Where combat fails for me significantly is Stealth. It's just too easy to accidentally overpower a stealth build in Skyrim. Enemy awareness AI is pathetic (Different than actual combat AI), and sneak attacks against them are brutally overpowered, with no real way for enemies to effectively defend themselves against a string of one-hit kills. Body awareness (Deus Ex: Human Revolution does this) and a faction+Region(IE bandits in the same dungeon) alertness sharing would make the stakes in stealth combat high enough as to fit the extreme (over)power it has.