I would say he's anything but a long ball specialist. He seems to have trouble tracking and/or adjusting to the ball on anything over 15 yards (the two drops he had on potential long gains were brutal, drive killing errors). He's also much smaller than even the slightest NFL player and goes down as a result of the mere idea of contact. Tackling is just part of business in football, but Atwell doesn't look like his body is under control when he gets flung to the ground.
I think he is being coached to hit the deck as quickly as possible. This technique needs refinement because sometimes it looks like he goes down too fast when another 2-3 yards are available.
It looks like his strengths are working back towards the LOS along the sidelines and falling or high-tailing it, out of bounds. He catches the ball well on those routes.
I wish he had Trishton Jackson's hands.