Awesome N7 armor. The helmet looks spot-on, and the arms aren't bad either.
However, the chest piece could use a little work with the strapping. It's not bad, but a few tweaks could make it better. The thigh plates also look like they need to be adjusted. I'd also recommend blousing your boots. Finally, the suit looks too clean, try scuffing it up a bit for a more battle-worn appearance.
But, I still have to say that suit looks awesome. I tried Me cosplay once (with a rather shabby Garrus rig). It took a lot of effort and it still looked kinda awful. You did a great job on this, and I hope to see more in the future.
For store-bought you certainly made it look good, the helmet in particular looks great!
But, the under-suit looks a little loose under your arm. and the suit would look better if it fit closer around the ankles. Right now I can't shake the impression that you're wearing dress slacks.
A final, really nit-picky note: your salute looks a little sloppy. It's not that bad, but if you take a look at real soldiers, they tend to do it much crisper. (of course, they don't have armor getting in the way)