I personally think that ACIII must be similar to ACII. Not only do I want it to, in all aspects (story, range of characters and soundtrack), but I feel - from the trailers - it will top ACII. I hope ACIII will have as beautiful a soundtrack as ACII had; ACII's songs are still some of the 'main' ones for AC:R for example.
Seeming though ACIII will be set over a course of 30 years (1753-1783) I think it will be like ACII's story in the sense that you get different, varied events, such as childhood, teen years, young man and - interestingly - old man. I say interestingly because 30 years is a LOT of life; it may be that after ACIII there will be a new 'numbered' AC, made by the Junior Ubisoft team (who made AC:B and AC:R). I don't think Ezio's three games had a story length spanning this long (allowing for him to continue realistically without getting too old for that many games).
Furthermore, do you think ACIII will have DLC's that are much better vaule for money. As in, rather than a few MP maps/new missions, do you think there could be space for things like new animals to hunt, an expansion of the current locations (maybe an expansion in the Caribbean location!) or even a supposed 'discovery’ tour in which somehow Connor goes to Italy (after the 250 years between Ezio and him), possibly unravelling Ezio's 'secrets'. That would be an awesome DLC; I think I'll forever miss Renaissance Italy as a location for AC. There could also be some PS3 exclusive DLC's related to going 'back to Italy'.
Suggestions on anything?