I believe most fans, casual to committed, have a very under-developed sense of how important weekly preparation is, especially for a quarterback. Wallace has spent all week every week trying to give the Packers D a good look at the opponent's offense. His time has been spent, week after week, studying the other guys' offense.
Putting a backup QB, and a new one at that, into a game where he is expected to run his own teams' offense, all the while being cramped by ultra-conservative play-calling and, tension, and paranoia over the health of the starting QB..... well...... not exactly a recipe for success.
Preparation is huge. I hardly think the importance can be overstated. The QB we saw last night was completely Unprepared, as was the rest of our team, as was our coaching staff. The degree to which Wallace was effective in helping prepare the Packers D is inversely proportional to the degree to which he himself was prepared to play against the Bears D.
Given a week of preparation, I fully expect to see something far more polished next week than what we saw this week.