And not just the ecstasy of Salford Red Devils' 19-18 golden-point win in the Million Pound Game, but also the despair of beaten opponents Hull KR.
If anything, it was reaction of the Hull KR players and their families that made the biggest impression on Kopczak.
"To see the wives and the families of the opposition crying and upset wasn't nice," he told BBC Wales Sport.
"It's not a nice position to be in and I wouldn't recommend it.
"You couldn't really celebrate and it was more a case of job done and get out of there."
And that after securing the most important win in the history of the club, who had been within minutes of losing their Super League status.
For the defeated Robins, it meant relegation and an uncertain future for the club's players, with contracts under threat.
With so much at stake in one end-of-the season match, the Million Pound Game has been criticised since its introduction in 2015.
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Hull KR's Ben Cockayne described the concept as "a disgrace" and said it hurt the Rugby Football League's efforts to promote good mental health.
Salford looked destined for relegation as the highly charged game at the Lightstream Stadium drew to a close.
They trailed 18-10 with two minutes left but Niall Evalds' try and Greg Johnson's score with the last play of normal time levelled the scores.
Gareth O'Brien's drop-goal in golden-point extra time secured victory to save his side from the drop to the Championship.
"At one stage I thought it was all over, but credit to the boys they dug deep and found a way to win," added Kopczak, who was among the Salford replacements.
"It's not good for the players but it is what it is. You've got to do it and someone's got to go down.
"Hopefully next season I'm not in that situation again. We've got a great bunch of lads and we shouldn't really have been in that situation."
With Salford's Super League status secured, Kopczak's focus is now on another challenge - captaining Wales' attempt to reach the 2017 Rugby League World Cup.
Wales, who won the European Championship in 2015, have qualifiers against Serbia at Llanelli's Stebonheath Park on Saturday and away to Italy on 29 October.
"We've got two tough games and it's going to be interesting," Kopczak said.
"But the boys are really up for it and we want to build on the success of last year."
John Kear's side will face Serbia and Italy without Wigan's Ben Flower and Rhys Evans of Warrington Wolves, who are unavailable after playing in the Grand Final.
Tyson Frizell, capped five times by Wales, is also unavailable having been included in Australia's squad for the Four Nations.
But Kopczak says his own Super League experience, as well as that of Salford team mate Phil Joseph and Widnes pair Gil Dudson and Lloyd White, will help Wales.
"It's for us to lead from the front and get ourselves in a great position to start with and kick on from there," Kopczak said.
"We'll focus on ourselves, get the job done right and aim for the World Cup."
Craig Kopczak leads Wales into their World Cup qualifiers against Serbia and Italy this month with the extraordinary drama of his club's Super League survival fresh in his memory.