Howdy peoples! Seen the movie yesterday and thought it was about average. Couldn't understand why the Avengers were the only ones fighting the invaders, especially since the aliens were so weak. If Black Widow's hand guns had no problem bringing them down I would imagine our troops would've laid them waste.
I forget the exact wording but the the two cops we meet trying to manage the chaos mention that "the national guard is on it's way or an hour away", not sure which. So no doubt had our military shown up then the foot soldiers could've been dealt with. The flying slug though was quite armored as even IM was waiting for chinks to develop before shooting them.
As far as the Helicarrier I'm guessing the planes on there were mostly damaged and/or personnel injured. Therefore keeping the Helicarrier out of the action. The unauthorized launch by the one with the nuke lets you know that the Deck was locked down for some reason(s). I'm guessing cause so much chaos was still in affect from the Loki breakout. The scenes are nearly back-to-back.