Part of the issue is the timing, it kills you when he decides to swing the attack, not when the attack connects.
Precisely. Particularly with the two-handers, it's extremely easy to dodge two-handed power attacks because they take a good second to connect while the attacker is immobilized, but if it results in a finisher, you never get the opportunity. The animation just has you staring at the hammer like a deer stares at on-coming headlights, even if you were barely in range while running backwards when the attack started.
I actually saw a Let's Play of Skyrim recently that highlighted this problem. The player was going toe-to-toe with a bandit, and was getting somewhat low on health. The enemy was running towards him (not attacking yet), and the moment the player pressed tab to bring up the menu, the camera switched to third person. The player used potions to heal up to full, and upon exiting the menu the bandit did a finisher and killed him... despite being in no immediate danger... simply because the game had already decided 'player dies now' before the fatal hit.