It's nothing particularly special. It's better than many anime movie spin-offs of TV series, but that's a low bar. Tomoko strongly disliked it, while I liked the last half-hour.
It's a good TV episode, basically, but movie-length. I don't mean that it feels slow. It doesn't. It's got lots of plot and action. However much of that is messy, poorly introduced and/or lacking in dramatic focus. It's original rather than an adaptation of anything by Hiromu Arakawa, needless to say.
The story involves three countries, a city and a very unnatural-looking valley that actually does get explained. Milos was conquered by Creta, then both of them were later conquered by Amestris. Table City, previously known as the Hill of Milos, is or has been owned by all three of these countries. These days the Milosians have been expelled from their sacred city and have to live in something called the Valley, which is a colossal artificial canyon that surrounds Table City like a dried-up moat. All this is actually quite interesting when you eventually work out how it all fits together and what it means for the people who live there, but until then it's like an attention-repelling device.
Fullmetal Alchemist's trademark brutality helps, though. This is still a universe where soldiers will round up civilians and then gun them down. What look like action scenes will often in fact be military operations that leave everyone on the other side dead, often bloodily. A little girl called Julia is put through horrors. Some of this film's last-act betrayals are nasty even for Fullmetal Alchemist, in fact, while there's also the Big Bad Blood Plan. Ew. There's some serious evil here. That improves things.
Dramatic meat emerges in the last half-hour. Julia gets pushed over the edge, the villains go nuclear and I ended up quite well-disposed towards the film, despite having snoozed a bit during the first two acts.
Tomoko hated it, though. She thought it dragged the Fullmetal Alchemist universe too far towards magic and superpowers, with for instance SPOILERing a SPOILER allowing the inexperienced SPOILERer far more spectacular abilities immediately than when we saw the same thing in the main series. That didn't bother me. However she also pointed out, correctly, that the Fullmetal Alchemist regulars aren't very important to the plot and you could write them out entirely without much trouble to make an entirely original movie. Fans got annoyed at Roy Mustang's token role, for instance. Personally, though, I thought the movie's main continuity issue was involving Winry in an alchemist superhero action sequence, after which it would be impossible to pretend in the main series that she's ignorant of what Ed and Al do for a living and so she'd have to be an idiot to keep getting cross at Ed for damaging his artificial arm.
It's set during ep.20 of the 2009 Brotherhood series, by the way, i.e. during chapter 11 of Arakawa's original manga. Not to be confused with the 2005 Fullmetal Alchemist movie that's a sequel to the very different 2003 TV series.
Even the art is iffy. It's well animated, especially in the spectacular action sequences and the wolf movement, but the art and character designs are worse than the TV series. They're crudely rendered and not even always accurate. Ed's blonde hair is black-lined, for instance, whereas in the Brotherhood TV series it had always been brown-lined. Alex Armstrong's brief appearance is a particular lowpoint. The best-looking thing in the movie is a train, which is cell-shaded CGI.
Is this a bad film? No, I don't think so. It's just mediocre and inferior to its parent TV series, as I tend to expect with anime movies. It's fine. I liked the third act, which is the most important one. I think you could distil it down to a pretty good TV episode, or perhaps a two-parter if you didn't want to lose any of the worldbuilding. Table City and the Valley are freaky and cool, while it's nice to have the Fullmetal Alchemist world expanded with a country we'd never visited before. There are also some things I liked in the earlier stretches, e.g. the satisfyingly slimy Peter Soyuz, or the way Al is more memorable and important to the movie than Ed. I loved the casual way he breaks his manacles as soon as it stops being the right thing to play along with his captors, while there's also his relationship with Julia and "I'll stop the lava". Awesome.
I wouldn't recommend this film. You're unlikely to think it's good. Personally, though, I'd call it a passable adventure with spectacular action scenes, really evil baddies and enough points of interest that I didn't think I'd completely wasted my time.