I'm not sure if some of these third instalments mentioned (such as Alien and Hellraiser) are correctly labelled as having 'lost it'.
Progression/evolution is more appropriate I think - otherwise we can easily end up with 'more of the same', time after time (Friday the 13th).
Halloween 3 is an extreme example, which despite being a very good horror movie in its own right, upset just about everybody with its irrelevance to the first two films.
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