I think thy're milking the cash cow too much. If they carry on making 1 game a year, people will become bored and it will become like COD....same game each year with minor changes....
While I didn't hate AC3, I think it was lacking. Heck, when I find Haytham Kenway more interesting than Connor, you know there's a problem with your main character.
I just didn't find Connor as compelling as Ezio. You got to see Ezio grow up and mature...but Connor, his growing up is too quick, and also he still remains quite brash and unlikable. He just doesn't have the same appeal as Ezio.
Plus, I didn't find running around Boston or the frontier to be as good as running around Italy in AC2. For me, I don't think anything in other Assassin's creed games could compare to the city and architecture in AC2.
However, I do give credit in AC3 for the improved graphics and animations.
As for AC4, I am a little concerned that they are making the ship battles a large portion of the game. I didn't like them in AC3, so I doubt I will like them in AC4, unless they make significant changes to the mechanics.
I can only hope that Edward Kenway has some kind of personality like Haytham or Ezio, I don't want another Connor.>_<
Also, I hope the assassinations will be like they were in AC1 or 2. In 3 they were basically chasing people around and then watching a cutscene. After all the buildup to Charles Lee, I was disappointed with how he was killed. I felt cheated. So I hope AC4 won't make the same mistake as 3.
I also hope they'll be able to portray pirate life as accurately as possible, none of the fantasy. But as of yet, we don't know much of the story other than Edward Kenway did serve in the navy, then becomes disillusioned and becomes a pirate instead to gain riches and glory.
As for gameplay, apparently there will be treasure hunting, swimming and animal hunting, alongside the usual assassination of key targets.
I'm sure it will sell well. AC3 had very good sales figures, regardless of how the game was in comparison to previous assassin's creed games.