A mix of New Age mysticism and Catholicism without the fun bits like aliens and hell.
One of the good things about US tv shows used to be that the UK was always a couple of seasons behind; this meant that if a plot seemed manipulative - with too many pointless mysteries, crass cliffhangers and characters dying just before they could impart answers - one could simply look at the episode recaps on US websites and find out what happens in the future. Like skipping to the last page of the book, this would divest the viewer of any compulsion to fritter away years of life watching tv.
When 24 used to be on BBC2, I saw into Jack Bauer's future simply by going to the 24 website. Apparently he did not die in the nuclear blast on his suicide flight over the desert: no longer any need to watch.
Lost presented such a grand mystery in the first impressive episode, but seemed to lack substance otherwise. I went to the ABC website and then to some forums but, unfortunately, though the US was a little ahead in time, there were no answers. So I posted a theory on a forum (the first time I'd posted anything on a forum) to see if anything rang true with others; it got attention and I got a little hooked on speculating on the show and stuff, in general. I posted 'The Ultimate Theory' - obviously wrong. I was conscious I might be turning into a character in The Machine Stops (short story by E.M.Forster) where people spend their lives in front of screens, turning into blobs, endlessly discussing discussions - prescient of blogs like this.
In the meantime, Lost proved it did have substance, mainly through the characters, using flashbacks to fill them out. There was a hatch; Desmond; Eko with his staff; Charlie and the drugs; a love triangle; a love rhombus; strange English accents; and all the rest - let's not summarize it, we'll be here forever. I think the spiralling plot got too much for the characters to bear, after a while, and still be interesting.
Over time, I lost interest and missed episodes; then felt compelled to go back and watch them just in case I'd missed some vital clue. I needn't have bothered; in my defence, by season 3 I'd taken to watching it at double speed to get to something happening. They must have criss-crossed that island a hundred times. As it turned out, there weren't any satisfactory answers at all.
Any reason for any mystery in Lost boils down to: an excruciatingly long chain of events, time travel, and there existing an inexplicable power source in the form of a glowing cave on an island. Everything proceeds from those irritating three things in Lost, we find out. But what makes you exhale audibly and gently shake your head in disbelief, in the end, is the actions of the characters. Faced with an existence in Los Angeles but blessed (cursed) with a memory of another alternate existence on a miserable island where they experienced loss, fear and pain, they instinctively choose to enter a [non-denominational inter-dimensional] church and die - albeit in a bright shining light way. Is Los Angeles that bad? There's a suggestion that Jack - and perhaps the rest - are dead already; except they're not - they just went on a different path after they changed time... in the past. No - don't get drawn into it - truly none of it makes sense. It never makes sense when a story pulls time travel out of the bag; add magic to that; and allow to stew for six seasons.
Lost represents a whole pantheon of dei ex machina recklessly negating any plot credibility or sense of peril. There was absolutely no reason for Jack to die on the island - but it's just, like, yeah, whatever.