"Het boek is leuk."
Translation:The book is nice.
Leuk is hard to translate accurately, it depends on the context. For books, I think "enjoyable" comes closest, actually.
You can have a book that's good, for which the description "leuk" would be inappropriate. Something depressing or very serious, for example.
Can this refer to persons as well? Een leuke man, a nice man?
If so, does it refer to one's personality or looks?
Yes, You can also say "een leuke man", and you can mean by that that he has good looks or is nice or both.