http://www.pajiba.com/seriously_random_lists/worst-4th-movies.php
This site ranks the worst 4th movies as:
7. Lethal Weapon 4: A lazy, mindless, tired and meaningless retread that wasted the talents of Jet Li and pretty much led to the pseudo-retirement of Joe Pesci, a once annoyingly minor character in the series used to the point of brain contusion.
6. Terminator Salvation: See Dan's review. A hamfisted, hokey sequel that came too long after the first three movies to rely so heavily on their mythology and yet managed to add little new. Completely witless and unimaginative, McG tries only to out-Bay Michael Bay and forgets to include the emotional center that made the first two movies so good.
5. Indiana Jones and the Kingdom of the Crystal Skull: A misguided and unacceptable return to one of the best trilogies of all time. The magic was sucked out of it, its cleverness stripped, and a once iconic character was rendered second rate.
4. The Next Karate Kid: A poor excuse for a film, basically a really bad and overly silly remake of the original with a female character (Hilary Swank) in the lead. It was a bad 90s movie that was too cheesy even for the 80s.
3. Rocky IV: The one with Dolph Lundgren. Overly jingoistic, even for the Rocky series, this unrealistic, overblown fourth movie completely wore out an already worn out Rocky formula.
2. Star Wars: Episode I -- The Phantom Menace: George Lucas ruins the most beloved trilogy of all time, transforming the series into a cold, dispassionate kids' movie, ironically ruining the childhood memories of millions of adults. A disgraceful embarrassment to the series that really should've been the end of it.
1. Batman and Robin: A campy Batman replete with homosexual innuendo, bat nipples, and not only the worst fourth movie, but the worst blockbuster movie of all time.