I enjoyed Mechanismo when it ran, I havent read it since. While I dont have memories of it being a stand out classic, it was a solid Wagner story in a sea of excellently drawn but ultimatly rubbish Dredd stories. I don't remember the Book of the Dead story but I do remember the art being excellent, great cover when the Mummy attacks Dredd. Likewise Frankenstein, excellent art.
The worst by Millar and Morrison involved Vatican city Judges, drawn by Mick Austin. Thankfully I cant remember the details, but it did involve some sort of talking carriage with a Thomas the Tank Engine face. Mick Austin is an absolutley fabulous cover artist, (Marvelman, Anderson anyone?) but God I couldn't stand his comic art.
Anyway, Mechanismo, well worth a read, leading into the hugely disappointing Tenth Planet/Wilderlands. As people have said, it did get Dredd to the current storyline which is the best in years.
David