Crap sequels and the like I can think of include:
Poltergeist II and III-unnecessary stupid rubbish
Jaws III and IV-same as above
Batman Forever + Batman and Robin-cartoony garbage
Every Harry Potter film after #2-they butchered their books unlike the first two
Halloween 3-6 & 8-just did not work for the series to me, especially #8 ugh! I forgot to mention the remake sucked too
Pirates of the Carribean 2 and 3-just were not entertaining like the first, which rocked
The Lion King 1/2-tried to reduce the original to comedy crap
Balto 2 & 3-just bad disney ripoffs
The Rage: Carrie 2-utterly stupid
All Planet of the Apes sequels and remake-they all were a slap in the face of the original to me
The Secret of NIMH 2-no need to elaborate, bottom of the barrel schlock
Dragonheart 2-what the above said
The Hitcher sequel and remake-uneeded trash
Salem's Lot 2004 remake-disgrace to the book and the Tobe Hooper 1979 original
X Men 3-very very very pathetic, compared to the first two
Firestarter 2-no words here
T3 and beyond-another unnecessary crappy cash-in
Tremors 3-the worst film I have ever seen
And these are only a few I know...
This is just my opinionated list and you do not have to agree with it.