Gotta say, up until the Covies showed up, it looked like the real deal. (Cardboard ARs aside.) The Pelican landing in the background in the background gave me chills. The minimalist approach really raised the tension.
Now for the criticism. I'm sorry to say that the moment I saw the Covenant, I lost my immersion. The CGI (while admittedly amazing for your budget) didn't sell me. They stuck out from the scenery and the movements just didn't look natural. (The Jackal looked decent.) Then we got to the combat scene. The violence was fake and over the top, and the constant deluge of F-bombs was unnecessary and unprofessional. I understand that heavy language is expected in such a situation, but when the dialogue consists purely of '****ing **** that mother****er! **** him!' it gets a little silly.
That said, I see quite a large degree of potential in your project. As noted before, I was completely hooked up until the Covenant showed up; and I felt that the nod towards the Halo 3 'Believe' videos was a nice touch. If you wish to speak more about your project, and to discuss the other pro and cons of it, I would be happy to oblige. :)
Honestly, it was great. I didn't think the Covenant stuck out too much. My only complaints are about the over-the-top violence (especially the head exploding), as it wasn't really necessary, same for the cursing. The rest looked really good.