If you think there's only a good choice and bad choice, you're wrong. There's dozens of ways you could play the game. You'll be rewarded for the following:
- Never using any magic spells beyond "Blink", and never upgrading any skills.
- Never upgrading any weapons.
- Never killing anyone.
- Sparing even your assassination targets.
- Never being seen, ever.
- Killing everyone!
- Upgrading your weapons to the max.
- Upgrading all spells and skills to the max.
Just mix-and-match. The game is really replayable, and not too long.