The first couple of books or so were pretty good (if a little derivative) but then it descended into thousands of pages of the following:
1) Arrive in a new world that is weirder than the last
2) Check it out for a bit
3) Bad guy arrives in world
4) Bad guy chases good guys
5) Move on to the next world
6) Rinse and repeat
It's incredibly rare that I leave a book unfinished but I'm sad to say that I did so with one of the Otherlands (can't remember which any more).
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