I simply don't know if the dictionary is good or bad, actually. I have a really large vocabulary so I don't look up common words, and I read a lot of fantasy fiction where words can be made up, plus there is the possible-typo issue --so not getting a hit in the dictionary is not necessarily meaningful, even if it is frustrating. I can vouch for it being easy to use, though.
Ideally the nook would use the unabridged OED
