I once went to a Maccabi Haifa soccer game with a couple friends. (It was the infamous one where the Beitar fans cheered Yitzchak Rabin's assassination.) I expected the game to be boring - in 90 minutes of kicking the ball back and forth, a soccer game contains only a handful of scoring chances. But it was actually quite interesting to see the struggles for control of the ball, and the strategies for advancing it.
That said, I saw one big problem with that game - and with soccer in general. It often happens that one team clearly dominates the game from start to finish. But due to the extremely low scoring of soccer, chances are good that they don't actually score. And if the other team gets one lucky shot, or else a penalty shot, then the better team can easily end up losing 1-0.
A variation of that possibility has caused much controversy in the ongoing World Cup. A single momentary mistake by a "keeper" (apparently that's what they call goaltenders) results in a goal, dramatically changing the game and the team's entire fortunes in the World Cup. In the recent England-USA game, for example, from what I hear England clearly played better overall. But on one weak USA shot, the ball took an unusual bounce off the English keeper's hands and into the goal. (Some blame the bounce on problems with the ball.) Just like that, USA turned a predictable loss into a "stunning" tie against a much stronger team. A similar sequence occurred in the Slovenia-Algeria game. What is the value of 90 minutes of intense play when the game is really decided by half a second of random luck?
In other sports, it is certainly possible for luck to affect the outcome. Indeed, the two worst referee decisions in history went against teams from my home state. Each resulted in a win for the opposing team, which went on to win the national championship that year.
But as outrageous as these incidents were, they do not compare in impact to similar incidents occurring at soccer games. In both baseball and American football, it is normal for each team to score 5 or 6 times in a game. A bad call is unlikely to result in more than one undeserved score. If that score was enough to change the outcome, then the game was already quite close. If your team was clearly deserving of victory, it would not have failed in its previous chances to create a large lead that no single error could eliminate.
In soccer, that is not the case. One goal is all a team normally scores, and it is also the margin of error caused by unluckly circumstances such as referee mistakes. Thus, it is much more likely that undeserved circumstances will decide the outcome of the game. That cheapens the effort put forth by the players throughout the game. In my mind, this characteristic makes soccer a less compelling sport than many of its competitors.