I enjoyed this film very much, but found many parts of it to be ironic.
Alienation, marginalization, and repression are very common themes in Ang Lee's films. In The Wedding Banquet, we see Wai-Tung, a man repressed by the cultural norms of society (especially in Chinese culture). We would expect him to struggle against the norms of society for the rest of his life, no matter what he did, however, we find that if he had just come out to both of his parents in the first place, he could have avoided this whole situation.
There is also a very ironic relationship between the "old" and the "new" in this movie. Wai-Tung's parents, as we would expect, are the epitome of traditional Chinese parents. All they want is to find Wai-Tung the ideal wife, well-educated and well brought up, to throw a traditionally extravagant wedding, and to live to see their grandchildren. Wai-Tung, on the other hand, supposedly represents the "new" generation, one that is liberated and exploring their true sexualities. At the end of the movie though, it seems that Wai-Tung's parents are actually more modern than Wai-Tung. Wai-Tung is stuck in the old traditions, insistent on preserving a facade of perfection and adamant that he not reveal his true identity to his parents. Wai-Tung's parents seem to be more progressive than Wai-Tung himself, ultimately accepting his homosexuality with very little resistance.
This film has an especially ironic and complex ending. The beginning of the end starts when Wei-Wei "liberates" Wai-Tung by having sex with him, and eventually getting pregnant. Wei-Wei later gives a long speech to Wai-Tung about how she needs to abort the baby to do whats right for the baby. In the next scene, Wai-Tung's father and Simon are bonding with each other out on a walk. Wai-Tung's father then reveals that he knows Wai-Tung and Simon are lovers, gives Simon his blessing, and asks Simon to keep it a secret so that he can still have the grandchild he's always wanted (which seems ironic in itself). At this point, I thought, "Oh god, his father is going to be pissed that Wei-Wei is actually not keeping the child, and all hell will break loose." However, in the next scene, Wei-Wei has a change of heart and decides to keep the baby, a critical decision that allows this movie to have such a peaceful ending.
Personally, I did not expect Wei-Wei to change her mind. All along, I expected a tragic ending, with Wai-Tung's parents possibly finding Wai-Tung and Simon in an act of lust, causing the movie to end with Wai-Tung forever disowned from his family. Wei-Wei's decision to not get the abortion, however, turns everything around and produces a happy ending in a not so happy movie.