The new formula introduces an extra knockout stage, the round of 16, with the top two teams in each of the six groups going through as well as the four best third-placed sides.
Portugal did just that, finishing third in their group and going on to win the tournament with a 1-0 victory in extra time over hosts France in Sunday's final.
Cristiano Ronaldo's side qualified for the last 16 with three draws and have won only one match in the entire competition over 90 minutes.
France coach Didier Deschamps said, however, that it was unfair to say the Portuguese won only by using the possibilities offered by the expanded format.
"Maybe Portugal did not win many matches but they did not make it to the final by accident and they won it", he said. "You can't take anything away from them."
The new formula produced tight games, with teams focusing chiefly on not losing, and also made the last group games an exercise in mathematics as much as football.
When Europe's governing body UEFA decided eight years ago to add eight teams to the finals, its then president Michel Platini promised the standard of the tournament would not drop.
The surprise runs from some of the five newcomers, with Northern Ireland making the round of 16, Iceland reaching the quarter-finals and Wales advancing to the last four, suggested Platini was right.
SPOILING TACTICS
"People were anxious the format might not work but it has worked," tournament director Martin Kallen told reporters.
"This has opened new areas for football. I think there will be a boom in those countries and I think we well see more kids there playing football."
UEFA's problem is that when middle-ranking teams face top sides, they tend to pack their defence and use spoiling tactics.
"There are teams playing ultra-defensively but they do that well. The smaller nations like Albania or Wales are defensively very well schooled. They see their chance in that," said Germany coach Joachim Loew.
"The 16 teams was ideal. It made for great matches from day one," he added.
A bigger tournament has meant increasing the number of ordinary, undistinguished matches to the point where they almost seem to merge into each other.
The 24-team format offers UEFA an extra advantage by attracting more broadcasters, which is the main reason why revenue at Euro 2016 has increased by 34 percent to 1.93 billion euros compared with Euro 2012.
The formula will continue at the 2020 finals and Kallen suggested UEFA might stick to it after that.
"We don't know yet but at the moment it's the format we're looking at because it's been very positive," he said.
(Editing by Alison Williams)
