Let's break this down section by section.
ANIMATION/GRAPHICS
I agree with the reviewer below me that the animation can be a little stiff. The backgrounds and buildings and even the exterior of the train, however, are stunning, and that rising and falling snow.... *gasp of delight*
SOUNDS
There's a lot of effort put into the VAs, everyone was natural, believable and I especially loved how suave that girl with the blue hair was (I forget her name D: ). The High Consul sounded almost like a basso profondo version of The Hunger Games' President Snow. I was about to say the music was great too -- until I saw Hitoshi Sakimoto in the credits. No surprise there. ;-)
PLOT
Although I haven't actually seen the full series yet (this is my introduction to Dual Arms), I like what I'm seeing so far. It's gripping, it's fluid, and the way I look at it, there are a lot of things that are either resolved in later episodes, or would have been introduced in previous episodes. There weren't any cliffhangers; the story started well with a background premise of negotiation and tension, and ended well too. It still got me wanting more, which is definitely a plus.
VERDICT (TL;DR)
Stiff animation, excellent voice acting, excellent choice of music, very gripping plot. I wonder if this is a thriller of some sort... At any rate, I can tell that you've poured yourself into it, and I shall watch the other episodes when I'm next able.
4.5/5.