I love SotN to death, but I can't help but feel that the achievements could've been better. What achievements would you implement into the game, assuming that there weren't really any limits on which tasks they could involve? 
 
Personally, I feel that sequence-breaking is a large part of games like SotN, so I think that it should be awarded and otherwise encouraged. As such, I'd implement a few achievements that'd serve primarily to get people thinking in the sequence-breaking mindset. 
 
- Collect the Faerie familiar before getting the Gravity Boots or Leap Stone. 
- Collect the Holy Glasses before getting the Spike Breaker armor. 
- Visit the Master Librarian before stepping through the door leading into the Long Library. 
 
I'd also implement achievements that encouraged aggressive or more inventive approaches to fighting bosses. 
 
- Defeat five different bosses within thirty seconds of entering their chambers. 
- Defeat five different bosses without taking any damage from them. 
- Defeat five different bosses without using spells or sub-weapons.

Well this one was an earlier XBLA release as far as I remember, plus it was made before achievements were even a thing, so I can see why it was a bit messed up.  
 
But yeah sequence breaking should have been acknowledged on that level, that's what I would have done. 

I would have liked an achievement like "Collect every rare drop in the game", or "Have every piece of equipment in your inventory." 
 
It was a really easy game to Complete. 
 
BTW, what do you mean by Sequence breaking?"