What are the differences between the difficulty levels?

I'm currently starting a New Game at 'Warrior' (hardest) difficulty level. I previously finished the game at normal difficulty.

What should I expect?

Specifically:

• How do the enemies get harder? Do enemy NPCs increase, or just have more hit points or deal more damage?
  
• What are the differences with the stealth mechanics? Will they detect me easier?
• Any enemy AI behavior changes? Do they become 'smarter'?
• Any other differences between the difficulty levels?