Terminator or Matrix or Alien sequels
what was most disappointing to you personally?
imo as much as I love Terminator and hated it seeing it flushed down the toilet again and again each post T2 movie had varying alarm bells beforehand (no Cameron, McG, PG13, Jai Courtney, SJW, dodgy trailers etc) so when the movies came its always been a sort of expected disappointment...
whereas with The Matrix (the 1st was just as impressive and awesome as T1/T2 & felt very much like an extension of those movies like a Terminator: The Next Generation) you had the same writers/directors/cast come back for not 1 but 2 sequels back to back BTTF2/3 style, so it was just assumed it would be like the T2 and T3(had Cameron directed T3) of The Matrix (especially with the awesome looking trailers).. and when they went "SW prequel" it was highly disappointing even more than the various Terminator sequels imo
i'll also add the Alien series (since Alien and Terminator have always been closely connected adult SF - the long gaps between films, Cameron, first 2 classics followed by disappointing sequels,etc) id say Alien franchise has been way more disappointing, as each movie held much promise more so than any post T2 sequel (especially Scotts prequels!) so when they weren't anywhere near that classic status of the first 2 it sucked!
so imo in terms of disappointment - id say Matrix, Alien.. then Terminator