(Please remember before you click that I'm going to have to give away at least some of the details of the setup in order to review this thing. Nothing specific beyond the setup and some vague statements about the plot arc will be given, though.)
To be completely honest, I went into the theater with very low expectations. We all went through Shambala together, which is explanation enough, and my reaction to the Milos trailers was basically, "Batman? Really? And I'm going to end up paying money to see this?" (Yes. Yes, I was.)
The bad news is, Milos isn't The Movie all fans hope for - the mind-blowing, fulfilling continuation of a beloved canon that we'd watch again and again. The good news is, Milos is a fairly solid offering all the same, putting favorite characters through familiar paces in a mildly exotic locale with a reasonably interesting cast of new faces.
When writing the story for Milos, BONES fell back on that old standard of the FMA video games: the era during which Colonel Mustang had the Elric brothers at his disposal to send hither and yon, investigating alchemical oddities. (Considering the number of video games, fanfiction, and filler episodes set during this period, which couldn't have been longer than a couple of years, one begins to wonder if Mustang has a time alchemist squirreled away somewhere. My money's on Riza "You're Off Schedule Again, Sir" Hawkeye.)
In a twist that also reminded me of the video games, the brothers endeavor to get to the bottom of a shocking alchemy-related incident (in this case, tracking down an escaped criminal who explosively broke out of jail with only a few weeks remaining on his sentence, taking with him only a newspaper clipping), and in the process become embroiled in a mysterious conflict (an ethnic rebellion in Creta, involving the ancient alchemy of the Valley of Milos) and help a troubled girl confront the demons of her difficult past.
All of this is nothing new, but it's handled with reasonable panache and flair, and for once the writers stay more or less within the bounds of alchemy as we know it (no angels or Gatebabies or leaping between dimensions, though the Milos Valley form of alchemy flirts with the boundaries of human transmutation in a way that raised my eyebrows). There are plenty of lovingly animated fight scenes, including an impressive set piece with a crashing train on a bridge (how does anyone convince the Elrics to board trains anymore?) and several chase scenes that take advantage of the unique architecture of Table City, that wedding-cake-shaped citadel from the trailers.
The new cast of characters are fun, and although you may find yourself wondering who filed the serial numbers off Yoki and recycled him as a minor villain, they otherwise feel fresh and engaging enough. The writers chose to parallel Ed and Al's sibling bond with another, more damaged sibling relationship in the form of our heroine du jour, Julia Crichton, and her older brother; it feels a bit like a rehash at times, but generally it works. They also took the interesting step of making Julia a love interest for Alphonse instead of Edward, and the resulting bond unfolds slowly enough to not feel too forced, particularly since it's based on one part rescue-romance and five parts mutual fretting about their bonds with their difficult, yet beloved, brothers. Julia herself is surprisingly appealing - she's intelligent, determined, has her own believable goals, and never loses the chance to pick up a gun and use it, if one happens to be lying around.
As for the standard cast, the movie tells us very little about them that we didn't already know (Edward cannot resist lending a hand to a lost cause, Alphonse loves his brother and cannot say no to a pretty girl, Mustang and Hawkeye are helpful in a fight, Winry shows up with a toolcase and a smile right when she's needed), but it has fun putting them through their paces one more time. There are a lot of cast cameos early in the film, but once the action moves to Creta, it's mostly the Elric Show, with Mustang and Hawkeye showing up to be Big Damn Heroes near the end and then...not doing much, really. There are a handful of very funny moments, and the barest whiff of shipservice for the EdWin fans, but Royai fans will have to content themselves with more of the usual office/battlefield back-and-forth and not much else.
In the end, the trouble with Milos isn't with what it is. As it stands, it's a fun enough romp that teaches us a little more about the world of FMA outside the borders of Amestris, and although it takes a slight turn for the weird near the end (and gets startlingly gory - who knew a human body contained that much blood?), it comes nowhere near the delirious strangeness of Shambala, or even the first anime finale. As a film released during the television run of Brotherhood, with the expectation of more films to come, it would have been a blast.
Sadly, Milos is doomed to disappoint fans of the series to some degree, not because of what it does, but because of what it doesn't do. As the first film after the series finale, it has a lot of fan expectations riding on where it might go, but it's trapped by its mid-series setting, and consequently it doesn't develop the regular characters any further, or teach us anything especially new about alchemy. It doesn't advance any ships, reveal any secrets, or move beyond the finale into any new adventures. It's just a standard, classic Military Dog-era adventure for the Elric brothers, and if you set your expectations no higher than that bar, I can almost guarantee you'll have a great time watching it. Just try not to grieve too much about what could have been.