It is certainly a powerful movie. I don't think it is one of Spielberg's best (I can think of several better ones*) but it is perhaps the most complex, less linear and straightforward (of those I have seen at least, which looking at IMDB I reckoned to be about half of those he made since Jaws... less than I thought). It tricks us at the beginning into making us believe that it will be a direct tale of revenge: one by one, the terrorists will be shot or bombed in increasingly suspensful and exciting ways, and at the end the good guys (or those that remain alive) will say "mission accomplished" and return to their lifes. The killings are indeed incredibly suspensful and exciting, to the point that once and again I found myself gasping or jerking at the moment of the shot or the explosion, even if I knew it was coming -a tribute to Spielberg's mastery. But after the third killing or so, things start to get amiss. Things don't go as planned; someone is killed even though he was not in the original target list but is a replacement for one of them; the motivations and sincerity of the mysterious French informers to the group become suspect; the hunters become hunted. The film ends with all the plot threads still open, as if making a point that there is no conclusiveness to the cycle of violence.
Many commentators have focused on the way Spielberg makes the characters doubt and question their own mission, and before seeing I had the impression that the film would leave us a definite moral or message, such as "if we use the same methods than the terrorists we become no better than them". There are a couples of dialogue lines of this kind, but never so explicit and preachy: Spielberg knows better than that. It is true that he displays a typical Hollywood-liberal-sensitivity in making the characters discover moral dilemmas in a perhaps unrealistic way for hardened Mossad agents**, but for me the main "message" of the film insofar as it has one was not a moralistic one in that line, but a deeply pessimistic one. Retail missions against Palestine terrorism are necessary for the survival of Israel, because if they were not done terrorists would only be emboldened; but if they are done, more terrorists appear with fresh cause for revenge and the violence never ends. The movie shows this dialectic but does not offer any way out of it***, and leaves therefore a very sad impression.
There are other important subjects that the film touches upon, but one I would like to mention is the significance the state of Israel has for a Jew. There are several explicit references to this, including one by the protagonist's mother and one by his boss near the end, but there is one moment that does not intend to make such a reference, and nevertheless worked as one for me: After the introduction to the film where the kidnapping of the athletes is shown, news clips with the news of their deaths are shown while the Israel national anthem "Hatikva" is heard in the background. I had not heard it for years, and suddenly hearing it in this context was extremely moving.
*I don't think any of Spielberg's "serious" films, excellent as they are, is as perfect as his earlier adventure masterpieces like the Indiana Jones trilogy or Jurassic Park.
**In fact I have read that paradoxically (or perhaps not) this has lead both pro-Israel and pro-Palestine commenters to criticize the film in a perfectly symmetrical way: the former complain that the movie is anti-Israel because it shows the war on terrorism as something that can be subjected to moral doubts, while the latter complain that the movie is pro-Israel because it portraits Mossad agents as people with ethical principles and conscience instead of as remorseless killing machines.
***Hey Cynical friend, I bet you would never have expected me to use negative dialectics, eh?