twooffour said:

What I don't get is why the bomb didn't blow up. Or it blew up, but only like a firecraker? I forget.

I guess you missed the part about not being able to change the past? The island blows up in the past, no plane crash in the future; plan did crash in the future, therefore island can't blow up in the past.

Initially season six seemed pretty amazing when the idea seemed to be that we were dealing with split timelines,

'Timeline A': Desmond doesn't press the button and brings down the plane.

'Timeline B': Bomb blows up the island resulting in no button, no stranded Desmond, and no plane crash. All the influences the island had on the outside world from that point on never happened, resulting in significant variations in the lives of many of the main characters.

I really loved the 'Timeline B' concept being shown through the flash-sideways, which really added to the disappointment when the show revealed that the flash-sideways were just the characters existences in limbo, and not actually a 'Timeline B'.