The show as a whole was decent. I probably wouldn't rank it more than average overall, but I can't say I didn't enjoy my time watching it. It hit some nice notes with some of the mystery and events that occurred throughout the show. The time travel portion kind of disappointed me though as I pretty much got the vibe it was heavily toned down so that a greater number of people could feel like they understood things.
The ending was quite meh, but I suppose there are a number of factors that contributed to such *shrugs*
If I had to give a rough graph of my enjoyment of the show, it would be high near the beginning and trending downward with some spiking down the line. First few seasons built things up well, and there were some nice things in later seasons (I recall one exceptional episode with Desmond), but I guess you could say something was...lost.
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There is no shame in not knowing; the shame lies in not finding out