The best thing I can think to say about the Green Bay Packers opening game loss to the 49ers is that it's over. It reminded me a little of their playoff loss to the Giants; in a matchup of two quality teams, only one was ready to play.
Penalties. In the first week with replacement refs, maybe the Packers did what only Eagles WR Jason Avant admitted publicly; "Guys are going to kind of cheat." There seemed to be a lot of penalties around the league in week 1, and maybe every team was pushing it to the limit. The Packers had 10 penalties for the game, and at least 8 in the first half, so maybe there was an adjustment on that front at halftime. Still, two penalties in particular (hold/pass interference calls on Jarrett Bush and Charles Woodson) helped extend 49er drives, and gave the offense fewer chances in the first half.
Offense. I was a little concerned about the offensive inefficiency during the preseason, Aaron Rodgers probably had his least productive preseason since he's been named the starter, and it seemed to have spilled over into the regular season. His interception was really bad, but otherwise his accuracy was good and the offense seemed more efficient in the second half. They weren't ready for the start of the season, and it showed against a great defense. I expect they'll play better in the coming weeks.
Defense. What a wreck, though it was nice to see that Clay Matthews is off to a great start (2.5 sacks).
The run defense isn't going to be great, but it was better than it looked (32 carries and 186 yards against). The two big running plays were a designed quarterback run by backup QB Colin Kaepernick for 17 yards (it set up a field goal) and I don't know what Dom Capers was thinking at the time. When Kaepernick came in, the Packers stayed in their nickel package (maybe it was their dime) when it was well known that Kaepernick was going to be used as a runner, and he gashed a spread-out defense. The other big run was Frank Gore's 23 yard touchdown, which came against a deflated defense after Rodgers's ugly INT. The defensive players still have to make those plays, but it doesn't look like a sign that the defense has some fundamental flaw. Otherwise, it took 30 carries to earn 146 yards (4.8 ypc), which is not good, but isn't a crisis either considering that the Packers seemed to be in their nickel package (only two defensive lineman) for a majority of the game.
The pass defense is the bigger concern, as Alex Smith gashed them for two touchdowns and a 125.6 QB rating (8th best QBR for week 1 as four sacks dragged down his rating). The penalties I mentioned above were part of the problem, and CB Sam Shields looked a little passive on the touchdown pass to WR Michael Crabtree. The big problem seems to be their middle of the field zone, where the inexperience at safety (Morgan Burnett and the combination of M.D. Jennings and Jerron McMillian) and inside linebacker (4th career start for D.J. Smith). Also, rookie LB Nick Perry lining up against any receiver in the slot is asking for trouble. There's no solution at this point, except to let those young players grow with more experience.