After losing, US goalie Hope Solo apparently accused the Swedish team of playing "cowardly soccer." Of course what they really did was play defensive soccer, the strategy that they correctly thought would give them the best chance of winning. There is nothing illegal, unethical, or unsportsmanlike about this, but it does tend to make for boring soccer, and produced the dreaded penalty shootout, which is always a bit like deciding the game by a coin toss.
The biggest problem with soccer has long been its defensive predominance. One can't imagine an American football game remaining competitive if one side had been reduced to ten players, for example. Because the defense has such a strong advantage, there is always the temptation for the weaker team to sit back and tempt the stronger team into over-committing, or just wait for the coin-flip like penalty shootout.
I suggest one modest change in the Olympic and World Cup rules which would get rid of the penalty shootout and many of the draws: go to Swiss system pairing and scoring (like that used in chess). In this system, there would be no groups but there would be seeding. In the first round, the highest seeded teams would be paired with the weakest, and future round seedings would pair like scores with like. All teams would play the same number of games, with wins scored as 3 points, draws as 1 (or maybe 4/3). The final round would pair the highest scores and first place would go to the highest score. All teams would play the whole Olympics and good teams would still be under pressure to attack, since a win would be worth more than two draws.