When you announce your departure, write a very logical and very true letter. Don't be afraid to say something like "I think my boss lacks the skill to delegate authority" or "the office kitchen is infested with mold". So long as you are truthful and logical, it can never be held against you, and it may even serve to prove your character as unwaveringly logical.
In no circumstances should you ever do that. It can only be used against you.
If you give me six lines written by the most honest man, I will find
something in them to hang him.
-- Cardinal de Richelieu
You former employer doesn't care about how logical you are. At best, you saved them EI payments, and at worst you just left them with a mess that will need to clean up. At best, you might want to grab a beer with a *trusted* co-worker to discuss problems. Doing an exit interview is only slightly less stupid than writing a letter.