I was really hoping that when they made the seafaring stuff for ACIII I was really hoping that they would take it and make a new pirate adventure series, I was pretty let down that it just became another Assassin's Creed title only because I was hoping to see a new property.
That being said I certainly think they've done a great job building the series and have built a huge fanbase that loves being able to buy the next title as soon as possible. I think this game came so fast because they made that sailing engine and it basically paved the way to do an entire game, it's the same thing that Saint's Row devs just did with the last DLC for Saint's Row 3, they started making it as a DLC and instead it became the premise of Saint's Row 4 that is coming out in August. Personally I have played every Assassin's Creed game and I thought they really didn't hit their stride until Brotherhood, I thought Revelation was a solid release and ACIII so far has been also a well done release. Assassin's Creed I have always thought suffers from the exact same problem GTA has, eventually even though you are in a sandbox things get very repetitive and the longevity factor in the game itself is heavily weighed on how much you enjoy the game world.
But as far as being "sick" of them that is certainly one persons opinion but I did notice you said you'd end up getting it anyways so certainly it can't be all that bad! At this point it just feels like Assassin's Creed is their brand name, they have 2 studios that work on the Assassin's Creed games so it isn't that shocking they are making games this fast, I'm sure we'll see a Vita game coming along side this one too. I think they'd be crazy to not make games at the pace they are if they continue to sell well and get good reviews. I am looking forward to this game because it's such a different step for them and there has been a massive shortage of swashbuckling, I sort of look at this like when Rockstar did Red Dead Redemption, I'm looking forward to seeing a studio that is great at crafting open worlds do something completely different that will still feel familiar.