Unfortunately, what was labeled a "co-op preview" turned out to have very little to say about the experience of playing with three other gamers. Instead, the article focuses on gameplay mechanics and level design.
However, Nate did have the following to say about the four-player co-op:
Admittedly, HAWX is a little light on the co-op strategy. We made attempts at coordinating our efforts but at 800 mph, that's a little tougher than it sounds. Instead it was more of a competition to see who could take down the most enemies (I won two of the three games we played). It was still more fun to be playing with teammates than without, but the difference wasn't as easily felt as it is in other cooperative games.
I hate bringing disappointing quotes to a front-page news post, but it is relevant, and it does describe the author's impressions.
Depressing news notwithstanding, I will continue to trod forward and bring you updates on this promising title. In the meantime, read the full IGN article for plenty of fresh gameplay details and impressions...