Okay, it's definitely going to be a hotly debated topic but here's my take:
The first Pirates of the Caribbean film was the only "good" one. As with many of these franchises. However, I still loved #2, mainly for Davy Jones. He was pretty epic, and I think (nearly) everyone can agree on that. One of the best movie villains since Darth Vader, in my opinion. And ultimately, though the plot was a little convoluted, I could still follow it, and found it fun.
#3 however lost me completely. I still enjoyed it on a completely superficial level, but I will not say it was a decent film, because it just wasn't. It was practically made of plot-holes, and the characters were, by that point, so far removed from their original incarnations, that I found myself not really giving a damn about any of them. Still, I've watched it several times, and I continue to enjoy it (mostly for Jack), even if I know it's not very good. Kinda' like why I keep going back to watch Cutthroat Island
That being said, I'm pretty excited for #4. Yes, it's probably too much of a good thing. But I'm holding out hope. Some of what I've seen so far looks fantastic... other stuff... well, not so much. But I will reserve judgement until I actually watch the movie.
When they started talking about 5 though, I can't say I was all that surprised. When they announced 4, it seemed to me that they were gearing up for a second trilogy of films. A good idea? Probably not. But it was pretty much inevitable. And hey, you never know, they could surprise us all and offer some really good yarns. Seems like they're bringing in some fresh blood and sloughing off some of the old, which could be a good thing or could be a bad thing, but there's no way of knowing for sure just yet. Naturally the movies will all be over-the-top fantasy films, and I'm sure they will continue to piss off serious historians and reenactors because of all the false ideas they put in peoples' heads, but ultimately, I couldn't care less about that. As long as there's a good story (which I haven't completely written off just yet), and some fun action and comedy, I'll be pleased enough. They DO create interest in the pirate community, as well as pirate history, and even if they perpetuate some untrue stereotypes, I can definitely get behind them for that reason alone.