I'm fairly sure I've never read 12 books in one series before (with the possible exception of Enid Blyton's Famous Five - which I read in random order with gaps, because they're all stand-alones). 
 To be honest, I don't think that even as a child I would have reached #12 in the Series of Unfortunate Events - which is not to say that they are bad books, more testimony to my need for change. 
 Anyway, I'm reading these to my daughter and we're in til the bitter end (Book 13). 
 This volume takes place almost entirely within the boundaries of the Hotel Denouement. Much of the humour derives from the fact that the hotel is arranged according to the Dewy Decimal system. I suspect that the author took more pleasure in this than his audience of ten year olds ... library cataloging humor being somewhat dry for children. 
 On the plus side we get to see many old favorites from other books, all summoned, whether villains or volunteers, to the hotel for a grand meeting / party. 
 Despite (or perhaps in defiance of) the title, don't expect many mysteries to be unfurled, or many story lines to come to neat conclusions. Confusion abounds, we don't know who can be trusted, what plans are afoot, or why. 
 The sugar bowl remains of prime importance ... be we don't find out the reason. 
 The already muddy lines between good and evil are trampled over still further. Our heroic children are called upon to do their direst deeds yet, including murder(ish) and arson... Good people come to the fore again, and fail, again. Justice remains blind. Doubt is even cast upon the Baudelaires' saintly parents. 
 Things come to a head and at the last the children escape in vexed circumstances, presumably for the last time. 
 One more book to go! 
 You should join my 3-emails-a-year mailing list for updates about my books. #prizes http://eepurl.com/cimnK1 
 ..