The PPL faithful showed their dissatisfaction when manager John Hackworth addressed the crowd after the final game.
Hackworth thanked them for their support and in turn heard something the home team isn't accustomed to - boos.
The coach is always a target when a team doesn't achieve up to fans' expectations. Regardless of how the fans expressed their dissatisfaction, they had every right to be disappointed.
That's because the Union were certainly good enough to be a playoff team.
They showed that by earlier beating the New York Red Bulls, 3-0, and last month going into Kansas City and winning, 1-0.
With 58 points, the only way Sporting Kansas City won't win the Supporters' Shield for the most regular-season MLS points is if New York beats Chicago on Sunday.
So the Union beat the top two teams in the Eastern Conference. They also recorded a tie at Real Salt Lake, a team that began Saturday in first place in the Western Conference.
Any team that can beat the best and compete with many others has the ability to make the playoffs.
The Union hit a tailspin, going 0-3-2, and were apparently in a free-fall, but then they won the game on Sept. 27 at Kansas City and the next week beat Toronto, 1-0, at PPL Park.
At that point it appeared as if the Union would make a final serious playoff push.
Yet it was the following game that symbolized this difficult-to-predict Union season of frustration. Needing a win to keep the heat on the playoff contenders, they laid a major egg with a 1-1 draw at D.C. United.
Yes, that was a United team that won the U.S. Open Cup, but it also has a 3-23-7 record, by far the worst in MLS.
Worse was that United totally outplayed the Union, who were lucky to get the draw on Jack McInerney's equalizer in second-half stoppage time.
This was a United team that was playing a lot of young players and didn't have Dwayne De Rosario, one of their top players, who was away with the Canadian national team.
The Union failed to play with urgency in that game, and it was a crusher. And they never regained their form.
Last week, the Union took a 1-0 lead at Montreal, only to lose, 2-1, while allowing the game-winner in the 84th minute.
The Union had the chances to cement a playoff berth and let it slip away.
So that is why nobody should feel great about the improvement this season.
So often it was mentioned how young the Union were, but some of the youngest players, such as 22-year-old keeper Zac MacMath or 22-year-old defender Amobi Okugo or 23-year-old defender Sheanon Williams, were among their best players this season.
MacMath, especially, came on strong in the second half of the season.
Despite the gains the team made, this was a season of wasted opportunities. And that is why any objective observer wouldn't call this a success, a fact that will become even more pronounced once the postseason begins and the Union are on the outside.