I still haven't watched the entire game, so I can't speak to every play during the Green Bay Packers first preseason game, but these two articles from the Press-Gazette confirmed the few plays I managed to watch.
First, CB Brandon Underwood is looking better and is in the lead as the nickel cornerback. He gave up some receptions, but he was targeted a lot. While he'll never be a shut down corner, he continues to improve.
Second, defensive coordinator Dom Capers admitted the "plan was to let them go out there and play." They were playing a soft coverage, it looked similar to a prevent defense, which as you know only prevents you from winning. The pass rush wasn't great, but it was a straight four-man rush minus their best pass rusher (LB Clay Matthews was held out with a bad hamstring).
I expect the defense will slip a little from last season: the run defense will remain stout, but I'm worried that they won't have enough pass rush other than Matthews. That will make them a pretty good unit, but I expect the offense will have to bail them out on a few occasions.