"This is awesome," Joe Staley leaned over and whispered to Daniel Kilgore during a recent team meeting.

The pair of offensive linemen watched as San Francisco 49ers head coach Kyle Shanahan dissected game film in the Levi's® Stadium auditorium. Shanahan broke down each play with meticulous detail.

The coach covered the responsibilities of all 22 players on the field. He explained which defender the offensive play call was designed to put stress on. Shanahan shared that on this particular running play, the slot receiver would determine whether or not it would work.

Each player knew their job, but more importantly, they knew how their role impacted the overall success of the team. Shanahan always explains the "why". That way, there are no excuses for missed assignments on the practice field.

"He's the smartest coach I've been around," Staley told reporters following mandatory minicamp. "(It's) his overall knowledge of the game, the way he sees the game and schematically how he constructs his offense."

Shanahan's premier football acumen is coupled with a standard that he established at the onset of the offseason program. Accountability is paramount and nothing short of maximum effort is acceptable.

That goes for Staley, the longest tenured player on the roster, all the way down to the undrafted rookies.

"He speaks very openly and honestly with everyone, and he's done that from Day 1. I think guys really respect that," Staley said. "He calls out myself or (NaVorro) Bowman the same way he calls out rookies. He expects the same out of all of us. No one is above anybody."

The level playing field has created an environment where each player arrives ready to improve on a daily basis. Call it pressure. Call it competitive nature. Whichever words you choose, the simple fact is that in a few short months, Shanahan has managed to change the culture in the 49ers locker room.

"I haven't felt like this in a long time at the end of the offseason program," Staley said. "The energy is back in the building – the excitement level and the attention to detail. I'm enjoying football again. I'm excited to come to work every single day. There were days the last few years where I couldn't honestly say that."

Staley has long admired Shanahan. During the coach's four-year run (2010-13) as offensive coordinator of the Washington Redskins, Staley saw Trent Williams evolve into one of the NFL's premier left tackles. Williams was Washington's first-round pick in 2010 and began his current streak of five straight Pro Bowls in 2012.

Cleveland Browns left tackle Joe Thomas was already an All-Pro player prior to Shanahan's arrival in 2014. Even so, he posted another All-Pro campaign in his lone season with the 49ers new head coach.

"I always thought it would be fun to play in his offense," Staley said, a five-time Pro Bowler in his own right. "I felt like it would be a great fit for me."

Staley's assumption has been validated, at least so far, and that's awesome.