Anti-climax: (for non native English speakers) is when a story is built and developed over a period of time, only to end in a trivial and a very disappointing manner.
There were many great moments on Lost, and yes, there were many disappointments, here is one:
in Maternity Leave (2x15), when Mr. Eko learns about appearance of "an other" being held in the hatch, he demands to see him and speak to him alone ... that whole sequence was built as if Eko was going to kill him ... only to simply say: "I am sorry" ... to me that was annoying.
what about you ??? any other bad moments on Lost?