"I'm impressed with a lot of the volume we have in," he said Wednesday. "I'm not impressed with how we execute it all."
The Cornhuskers practice again Friday and then go on spring break. They'll return March 30. In the interim, Riley and his staff will study practice video and pare back the number of plays they'll work on the rest of the spring.
"We actually have to pull back a little bit and focus in on stuff to finish with," he said, "so we head into fall camp being pretty good at a few things and not average at a whole bunch of stuff. That's my biggest concern."
The ground game appears to be in good shape, and De'Mornay Pierson-El is the best of the receivers at running the jet sweep, which is a staple in Riley's system.
The passing game needs polish. Riley said the quarterbacks need to complete a higher percentage and cut down on interceptions.
"We've got a lot to learn — if we're going to do more drop-back passing — about reading coverages and knowing where to go with the football faster," Riley said. "They have to see it quicker and get the ball out faster. Otherwise, we're going to get sacked a lot."
Presumptive starter Tommy Armstrong Jr. stood on the sideline for Wednesday's practice because of tightness and spasms in his lower back.
Armstrong said he and the other quarterbacks are struggling with interceptions because they tend to fall into habits learned in the offensive system under the previous coaching staff. He said he was accustomed to receivers adjusting their routes certain ways depending on the coverage.
Pierson-El said new route adjustments will be learned once the players delve more deeply into Riley's offense.
Until then, Armstrong said, "When we call one play, that's what the play is going to be."
Even things that would be considered simple, like quarterback cadence and calling plays in a huddle, must be learned. In the past, quarterbacks signaled for snaps by clapping, and the Huskers called plays at the line of scrimmage.
"It's not hard for me because I've just got to stand back and let those guys form a huddle, get the play in and let them know what it is," Armstrong said. "Certain guys on the team needed to get used to running back and getting into a huddle rather than running back and getting on the line. It's nothing major for us. Just have to get used to it."
Pierson-El said the second half of spring practice will be better than the first.
"It's going to take longer than two weeks," he said. "We need more reps and time for all the pieces to fall into place."