Firstly I want to say that this short definitely is an effective proof of concept and I would be surprised if this doesn't get turned into a feature in the near future. If I were an investor I would back this concept without a doubt.
Here's my feedback:
I liked the camera movements. The opening shot of the camera moving in on the two characters comes to mind as well as when the soldiers are about to breach and enter the area. The camera moving really makes the whole thing feel alive, which for this type of film is very important and something that more up and coming filmmakers need to remember. Excellent composition of the shots. I really liked the wide shots.
I was intrigued by the story and it's mystical elements, something which I enjoy. It makes me want to know more about this world that the characters inhabit.
The two actors that really stood out for me were the male and female leads. Finding the right actors is one of the most important aspects of a film and you have chosen well.
Even though the music is from The Dark Knight Rises (I know it won't be in the feature) it fit the short well however in some parts the cuts between the different cues are too abrupt. I think the part where the gauntlet is about to be used the music should be taken out completely because the sound effects are really effective and they would have stood out much more if it was just the sounds without any music. The music building with the tension of the soldiers approaching was where that the DKR music really fits.
The CG effects were designed and executed very well. I liked the impacts on walls from soldiers being thrown against them. It shows that you and your team thought about how these kind of things would impact upon the environment around them so this sells a bit of realism with the science fiction elements. The effects of the gauntlet are effective. The way the giant Mech moves reminded me of ED-209 from Robocop and made me smile.
Overall this is an excellent short. It had me grinning at the cool action set-pieces. The costumes, props, sound quality and production values show that you are a filmmaker who knows how to put something together that's professional.
Best of luck with this and I hope that your goal of turning this concept into a feature is realized and a success!