Well shit, way to make this the hardest damn critique I've ever done.
Vision: What to say, what to say... First, I must say that your style is getting much better overall from a first glance, and you should be proud of that.
Originality: I have seen Derpy, I have seen Halo ponies, but never have I seen the two out together like this before. I am a massive fan of both Derpy and Halo, so it is really hard for me to think of any constructive criticism. That being said, I am finding something very odd about the fact that she is standing on her hind legs and actually holding her Assault Rifle, when it would make more sense for her to be on all fours and have the gun maybe harnessed to her side somehow. I do like the bubbles on the chest plate and the smily on the gun, but the aforementioned issue and the fact that she has no visor are kinda tearing me out of the picture a bit.
Technique: Not much to say here, but I can tell you that your technique is really improving. I especially like how detailed you made her wings, and the smoke from the gun barrel was a nice touch. Coulda used a background, though.
Impact: Overall, not as astounding as some of your previous work, but speaking as a MLP and Halo fan, I do like this picture, and it will be going in my favorites and on my iPad.
Overall: A great little picture, with only a couple of design decisions that I think should be remedied if you ever decide to do something like this again. In case you were wondering, I have a bunch of pictures that I have uploaded, and if you ever have the time I would like you to do a little critiquing for me.
Thanks again! Just as you said, I've seen Halo ponies. but i wanted something different. so i went for a more Anthro style, was running out of ways to symbolize that it was indeed Derpy so thats why i left the visor out And for the background.. well ive said it before.. but i really am terribad at backgrounds lol..
also yeah anytime you want my opinions just shoot me a note with the pic and ill give ya a critique!