Based on the information provided at this time, it seems to follow the Harry Potter First Years in terms of unlocking characters, style of gameplay, etc. I think TT learned their lesson with Indiana Jones 2.
@operand: I agree with it following Harry Potter Years 1-4. I have Lego Star Wars and that is an improvement over Indiana Jones: The Adventure Continues, Examples are that I note: 1) Cheat Codes are similar to Indiana Jones 2 which I find is a good thing; 2) The HUB area is similar to Batman with the 2 zones; 3) Characters are purchased either walking around the HUB or through one spot where missions/levels are chosen. In the regards to the HUB's for Pirate's of the Caribbean: The play should be presented in this order: Curse of the Black Pearl, Dead Man's Chest, At World's End, On Stranger Tides, unlike the Indiana Jones Games which the first should always have been Temple of Doom, Raider's of the Lost Ark and then Last Crusade with the second game ending with Crystal Skull, which is the chronological order of the story.
Having played a demo of this at Best Buy and having played all of the other Lego games, I can say that Lego POTC doesn't at all feel or play like Lego Indiana Jones 2. The gameplay of POTC reminded me of a mix between Lego HP and Lego SW. I actually really enjoyed playing the demo of POTC and I'm looking forward to getting the game.
There is now, a demo on Xbox Live(I don't own a PS3 so I don't know about PSN) So you can try the game for yourself. However, as others have stated, this game does show quite similar gameplay mechanics comparable to Lego Harry Potter, and the Newer Lego Star Wars the Clone wars. The Lego games do seem to be making improvements with each new franchise mockery. I must say though, I really appreciate that in Lego POTC Jack sparrow walks/runs/moves like he does in the movies, as well as sounding(grunts and such) very much like he does in the movies. Although so far it seems like they are changing story elements to fit the Lego gameplay(try the demo and if you are familiar with the movies, you will immediately recognize these parts also.) Yet as far as the demo is concerned, non of these 'changed elements' is really a bad thing, just different. Bit longer of a post then I meant to type, but no matter.