First of all, all the comments bellow are comments about ACIV as we know it stands now (29/5/13) - which is not a lot, hence some of the concerns.
Primarily - what's the point? ACI lead into ACII with the messages left by Clay, ACII into ACB with Minerva's message, ACB into ACR with the stabbing of Lucy and ACR into ACIII with the synch nexus and the grand temple.
ACIII into ACIV seems...a stretch. Arguably the plot, the story of Desmond is over, if the series was a novel I could see this as an ending and we'd move on. It seems very odd to switch protagonist part-way through a series (in an obvious way, many other games do it in a subtle 'reincarnation' or unemployment/re-remployment way).
Yes, Juno has been 'released' on the world and everything that goes with that, but is that going to be the main arc now? Trying to take down 1 Precursor? Because as we know before in a war between humanity and TWCB, man did quite well considering their disadvantages, so is the next 3-4 game story arc going to be chasing down Juno?
If so then why this approach?
We know we're playing as someone inside abstergo (my fear of that being first person play notwithstanding) and that seems to be a real departure. The game has always been (ultimately) about the story of the up coming end at 2012 and the struggle of the Assassin's to prevent the Templar's seizing control. Now the perspective of this game seems to be - well we've run out of modern day assassins, there's about 6 of them left (active) so we're going to leave the assassins and start using up Templars.
I see the game becoming more Templar sympathetic too. I think it's great how even in ACI there were comments about how Altair was killing people without knowledge of a larger plan, and just killing off templars might not be the best tactic. In ACIII we very obviously saw the assassin/templar division become more permeable. IWith the modern day story also being biased towards the templars in ACIV, it is possible that they are encouraging us to see that 'nothing is true' when it comes to the greater sides of the war.
If the game is going to be a hunt down and kill Juno game (which I assume will involve some POE) it seems odd to be playing as the character that we are, Edward. I can only assume that this is because there is a great tied up mystery between Edward/Haytham/Connor which will be areal story shocker. But it seems more like, in order to use the same mechanics vis-a-vis naval play, they have favoured a similar time period to ACIV. Considering that boats have been around for many years before and after the 1700s, I'm a little disapointed in this choice.
Further the glyphs and rifts added a real nice taste to the series, almost reversing the 'nothing is true' statement by saying that all these mythological stories, King Arthur, Sigmund, etc, were true (or rather the truth is different to what the stories say but the stories are not fabircated). Maybe it is too ambitious, maybe there is too little information, maybe they are worried it could go down the wrong path but I am surprised that it does not appear to be something discussed further? A nice real-world interpretation of those time frames, a realistic nordic story based around Sigmund getting the sword POE, a realistic story around the parting of the red sea, a realistic re-imagining of any of the folklore-y parts would really give AC a new edge again.
ACI and ACIII were fantastic for giving an alternative story, or rather a more complete one, than the popular Crusades or American Revolution. ACII, ACB, ACR popularised a relatively unknown time perioid (politcally speaking. Most people are familiar with Leonardo but how many people knew about the Borgia conspiracy?). In ACIV they seem to be arguing the 'truth behind pirates' but we know they were rebelling against the establishment, we know they did quite horrible things and the reason films and pirate genre pieces dress it up is because it was horrible. It will take a fair bit to impress me in this next time period.
Don't get me wrong, I loved naval play in ACIII, I am a big fan of the series in general, I like the direction, I like the novelty and I like how 1 series can blend 4 time periods (inc present) into 1 universal game style. But this next game worries me. (Especially calling it ACIVBF - it sounds like they wanted to call it Assassin Creed: Black Flag but reaslised after ACR less dyed-in-the-wool fans wouldn't buy it, so added the IV. Seems an odd departure)
My concerns about the modern day arc may or may not be unfounded, it just depends on the info we hear about this abstergo angle. (PLEASE NOT FIRST PERSON PLAY)
We shall see how this develops....