Disappointing/under performed means something different to me than what seems to be the direction of this thread. The first team that comes to mind is the 2009 Liberty team - they were the defending state champs and brought back Anthony Gonzalez, Jarrod West, and Dante Holmes (who I think all were 1st team all state that season), started the year ranked #6 in the state, but finished 6-5 and got their doors blown off in the first round of the playoffs by Easton.
In that regard, 2012 Easton started the year 8-0, including beating the hell out of Parkland (D11 champs) and Pennsbury (SO champs). Team had four FCS guys and a ton of PSAC players. Quarterback who won the job got knocked out with an ankle injury and Shane Simpson broke his leg in week 9 after 1,100 yards in eight games. They absolutely fell apart against Parkland in districts. Parkland got beat up by a non-invincible LaSalle team, and Easton with Simpson that year was significantly more talented.
Now, if we're talking about the best teams that didn't win/get a shot at a state title, that is a different, and more interesting list. Statewide, somebody mentioned the 1996 Penn Hills team that was the returning state champ, #1 in the country and on a 28 game winning streak, and lost in the first round of the WPIAL tournament. Frankly, that season was set up to be Penn Hills-CB West, but the Bucks got upset in the first round of districts too. 1988 CB West was the runaway #1 team in the state, but tied CB East on Thanksgiving, which kept them out of the inaugural state playoffs (undefeated and untied Neshaminy got the District 1/2/4 spot). Gateway in 2008 was the all time shocker. Bishop McDevitt in 2005 is the biggest injury in state playoff history with LeSean McCoy going out. They walk to a title otherwise (I bet he makes up one point against McKeesport).
Locally, there are two big ones. Parkland in 1999 was the clear #2 behind CB West all year, and that would have been a hell of an Eastern Final. The Trojans went 10-0 and had an average margin of victory of 29 points. Sean Bleiler was the running back, he was a captain and fullback at Delaware when they won the national title. Tim Massaquoi was their receiver, he was a top 40 national recruit the next year and eventually played in the NFL. Defense had guys who played at Navy, Pitt, Penn, and Lehigh, three Division I linemen. Quarterback played basketball at Navy and was an all state hoops player (great athlete). They beat Easton 42-13 in the final game of the regular season. The next week, Easton upset them 7-6 in D11 semis. Season over. Easton went on to lose 21-20 to Becahi in finals in another classic, then Becahi played the all timer in Goodman with CB West (the punt return game). Parkland would have had just as much, if not more, of a chance than the Hawks in that game.
Speaking of Bethlehem Catholic, 2001 was their ultimate lost opportunity. Probably the best offense in the state - Mark Borda had nearly 2,000 through seven games with skill players that went to West Virginia, Penn State, Lehigh, Lehigh, and then JUCO legend Eddie Scipio (who missed the first three games of the season, which stopped him from the only 1,000/1,000 season in state history - he had 900 rushing yards and 800 receiving yards in not a full season). Then, Borda, two offensive linemen, and their leading tackler got kicked off the team in week 8. They still torched the D11 playoffs after moving Adam Bednarik from receiver to QB. But they choked away a lead against Cumberland Valley in the state quarterfinals. Bednarik threw three picks in the second half of that game. Full strengthen Becahi certainly was good enough to play with Neshaminy and Woodland Hills, but they made their own bed.
