Why is the script so poor?

I do have a love for all the Pirates of the Caribbean films, but there's no question that the 4th film in particular fell a little bit flat. People have offered up all sorts of reasons as to why they did not enjoy it - below par acting, too boring, iffy plot, etc. However, I tend to think that none of those criticisms are particularly fair and, in reality, everything is on par with any other PotC film, except for 1 thing . . . the script. Sadly, it's the quality of the script which binds all these elements together in order to make a movie great, yet here the script is just, to be frank, poor. As such, it devalues everything else and creates the illusion of poor acting, boring plot, etc and so on. If the script had been up to the standard of the 1st 3 films, then this could've been just as good as the 1st film.

I'm glad they didn't make it just another sequel as they would've fallen into the trap of the 2nd and, in particular, the 3rd films whereby they're forcing themselves (misguidedly in my opinion) to going "bigger" than before, thus upsetting the very formula which made the 1st film so great.

But why is the script so bad? I just don't get it. All the ingredients are there to make a really special Pirate flick, yet the script does not seem to have been given the same level of attention as in the other 3 films. Even in the 3rd film, which almost collapsed due to an over-complicated plot (which does improve after a couple watches I might add, which is great) it is saved by the quality, & authenticity, of the writing. It makes it all believable and of the period, despite being far out and driven by myth & legend. The 4th film really fails here, and by losing that credibility in the writing, suddenly those mythical topics which were so easy to accept in the other films (such as cursed treasure, Davy Jones & the Kraken, etc) in the 4th film they feel silly and exaggerated (the Fountain of Youth, Mermaids, etc)

Knowing the importance of a good script, such an elementary slip-up seems almost unforgivable and, for me, makes it difficult to watch despite me ultimately enjoying the content. The whole reason I love these films is down to my own fascination with Pirate lore and 17th/18th Century English history, and for the script to suffer from such a lack of authenticity (simply dropping in the occasional, clichéd "ye" just doesn't cut it I'm afraid) it just ruins the experience.

The strange thing is that the guys behind the Screenplay of On Stranger Tides are the very same guys who wrote the 1st 3 films, so why was the 4th so vastly inferior in this area? All I can think is that it is down to the director, and when you see his portfolio you kind of see why. Rob Marshall knows how to direct and, essentially, he does a decent job but surely it's up to him to identify the scripts inadequacies and rectify them for the big screen - what works on paper, after all, does not always work once on camera. His previous work is all fairly serious drama, and swashbuckling pirate fare and action just isn't really his bag. I just wonder if, as a consequence, he focussed his efforts on getting that right and ended up not giving something as fundamental as the script the proper attention. I can't help think that, had Gore Verbinski been in charge, someone fully comfortable in this genre, such a mistake would never have happened and, with essentially the same plot and acting, the 4th film in the PotC series would've been 1 of the most successful.

With all that in mind, I can't help my concerns with the 5th film. This time tho m concern is not with the directors, I think Ronning and Sandberg a well up to the task at hand, but I don't get the switch in the screenwriters. Sure, Elliot & Rossio ballsed up the script for the 4th film, but they got it right the 1st 3 times and, in combination with the right director, the 1st 3 films prove the formula works. Jeff Nathanson has the honour of penning the 5th instalment, and his back catalogue is pretty patchy. He can certainly write decent action blockbusters (as he has shown with the Rush Hour films) but I really want the 5th film to nail that authenticity in the manner the 1st 3 managed, & I'm not convinced Nathanson's writing will succeed in that, which puts a lot of responsibility on the director's shoulders.