Strangely, I have pretty much no desire to see this. As flawed as the whole franchise is as a film series - Curse of the Black Pearl being surprisingly competent, Dead Man's Chest being pretty horrible, and At World's End a crazy mess that somehow manages to stick the landing - I thought it achieved a nice bit of closure in its final moments. Still... this is Disney, and if there's one thing they like more than money, I don't know what it is.
The exodus not only of Bloom and Knightley, but of original director Gore Verbinski (who's most recent film Rango I enjoyed much more than any of the Pirates trilogy) will also mean it really will feel different as well. Obviously, there'll be attempts to keep the tone relatively similar, but don't be surprised if Penelope Cruz and Johnny Depp randomly breakout into song and the scenery changes to an empty stage: that's Rob Marshall's trademark... -_-