"The goals were missing. We were greedy," Müller said after the 1-0 win that ensured Germany finished on top of Group C.
"There were improvements in our play, but of course we aren't 100 percent happy.
"The goals were lacking. I alone could have drawn level in the scorers' list."
Müller and other German players were upset at the criticism they faced after labouring to a 2-0 win over Ukraine in their first game and then a 0-0 draw with Poland.
The Bayern Munich striker, who set up Mario Gomez for Germany's goal and hit the woodwork twice in the first half, was sure there was improvement.
"It was a step forward and a very committed performance," he said. "We had more chances than in the last eight games."
Coach Joachim Löw also bemoaned missed opportunities.
"We created some very good chances, but also squandered a few.
"They had no chances, but we needed to have had more purpose and consistency in front of goal. It was good in terms of the football we played, but we should have been more dominant," Löw said.
"We played well and we were convincing but we didn't score nearly enough. That was really lacking today," said Mats Hummels.
"When we play against the really top teams we'll have to give it that little bit more."
Germany should have scored more, but gangly striker Müller was at the heart of the improved performance at a Parc des Princes awash in Northern Irish green as he slipped passes to Gomez and Mesut Ozil or headed just over the bar.
Müller had shown irritation with the always demanding German press ahead of the game.
"You have rarely been impressed with our results - apart from the 7-1 against Brazil (at the World Cup)," he snapped.
"We expect a good performance, but we can't guarantee the result.
"It's without question that we're favourites against Northern Ireland, I would take a tough win and tolerate what's been written (about us)."
While the Germans were still far from their sparkling form in Brazil, their domination on Tuesday put rivals Spain, Italy and France on notice that they mean business.
Germany now move north to Lille where on Sunday they will take on the third-placed team from either Group A - Albania - or B - Slovakia - or Portugal's yet-to-be-completed Group F.
Müller will be happy to hear that UEFA has ordered the pitch in Lille to be relaid after a barrage of complaints about the dried-out surface.
But from the way he was roaring at and cajoling teammates in Paris, the pitch will be the least of Germany's opponents' worries - it looks as if Die Mannschaft are just revving up.