It's not a quite a trailer, and there's no way to know if it is actually gameplay, but if it is, IronFall for the 3DS is an impressive piece of tech.
The game takes some very obvious cues from Gears of War, but on a much smaller screen. The video showcases a third-person shooter with bulky armored soldiers, but you might not know it was a 3DS game without the handheld's frame embedded in the video.
The video promises 60 fps, impressive lighting, physics, and particle effects, detailed character models, and large buildings falling apart. We'll have to wait and see if the game lives up to the impressive tech shown in the video.
Developer VD-Dev has created some technically impressive and surprising game's on Nintendo's handhelds in the past, like a fully 3D versions of Stuntman and Driver 3 on the Game Boy Advance.
IronFall should be available spring 2014 on the 3DS.