My big beef with the Chitauri was that if Natasha could take them out with a 9mm handgun, they were hardly any kind of threat whatsoever.
Well, let's be fair. She could have had a .40 cal.
But BW is supposed to be an expert marksman so she could've been hitting them in their "one vulnerable spot" like in the face/mask or something. But, yeah, I agree that they were so easily taken out by an earth handgun was weak. But along those same lines those soldiers may have just been "cannon fodder." They're meant
to just go in and get killed to keep those they're invading overwhelmed by sheer numbers while the bigger guns (the ships) do the heavier destruction work. They're not meant to be formidable or even unstoppable as single soldiers in battle they're meant to simply overwhelm by numbers.
So what if the puny Earth handgun takes one out? There's 10,000 more where that came from!
I did think it was awesome how BW managed to get ahold of, and use, one of the Chitauri weapons, also loved it when she boarded the Chitauri air-skiff, back-mounted one of them attacking... Aww, hell, I loved everything BW did.