. . . . so is he Altair or Desmond?? or both?

 Not familiar with the game (don't play video games - not puting them down - my hand eye co-ordination is not quick enough to be a proficient player).   I grew up pre-video games, playing the standard old sports which require different skill sets.  The trailer is nice to look at...great computer graphics.  I'm a little tired of story lines where the good guy beats the crap out of 20 or 30 bad guys at the same time. (the badees can't figure out how to shoot him - even when he's just standing still in their midst looking menacing).  Heck if the guy comes from the future couldn't he bring some modern weapons with him to make his heroics slightly believable.   The hero doesn't seem worried that his interference in past affairs could screw up the future nor does he seem all that bright.  Even though he knows coming from the future that the patriots ultimately win their struggle with the redcoats (without his help) he can't resist getting involved.  It's good to see that like Superman he fights for truth, justice and the American way.

the assassin in the past doesn't know of the future.  the guy in the present, desmond, is trying to figure out what the deal was with these assassins in the past so he uses a machine that taps into his dna's memories of what happened way back when.  so each battle in the past is a memory pieced together by desmond without future knowledge for the assassin, just good ol butt kickin know-how.  so desmond gains skills from these memories and tries to uncover a conspiracy that's unraveling in the present.