As has been said before, this version is very, very closely following the events of the source material(to the point of including the annoying techniques used to convey humor in manga much more often than the previous series), while the first version diverged significantly after the events of the upcoming episode. The story is about to become quite different in a real hurry.
There were also a lot of anime original episodes by this point in the first show, which is why episode 12 in this version will correspond with episode 27 in the first. I think a lot of the problems people are having with this show stem from the fact that a lot of added material, both completely new and expanded versions of minor events in the manga, went into the first version in an attempt to develop the characters, while in this version we're still very, very early in the story.
21 chapters covered in 11 episodes - 2-12, with 75 chapters yet to be covered. 3/4ths of this new show will be almost entirely new material. One potential problem I see is that they're really rushing with this first section, exacerbating the already limited character growth present in the source material that the first version took considerable liberty to improve upon.
I hope they slow down now that it won't be rehashing what was already covered. If they slow it down to 1.5 chapters per episode from the current 2 per episode, that should leave them with 45 or so uncovered chapters at the end of this show, plenty of material for 24 episode continuation.
One big difference I'm noticing is that the pace, and adherence to the source material, is dramatically increasing Winry's screen time, certainly a change for the better. She could convert the deaf and blind to blondes for lifers. And of course the OP is fucking awesome.