If Lois's instincts told her that Clark was a desirable, attractive guy that she very much wanted, then her instincts should have warned her off Lex more than they did. Yes, like some of you pointed out, her instincts did make her reject Lex in the end. They didn't totally let her down.
For me it works like this. We know that Lois social life is extremely limited “she has interviews not dates”. This bugs her because she craves success and being seen as successful, being the girl who hasn’t her dance card filled isn’t what she wan’ts to be perceived as. And suddenly the richest man in America comes and asks her for dates,
Here you have a guy that clearly has options yet chooses her, Quite obviously he is a tremendous boost to her ego irrespective of any attraction she feels to him. And he is funny, interesting, cultured, not difficult on the eyes, seriously what woman wouldn’t ask herself if she makes a mistake discarding such a man?
And I mean how different seem they to be? They are both ruthless go getters. (People just doesn’t now how ruthless Luthor really is.)
But this isn’t enough, Lois is perfectly content to soak up the attention, but she is guarded when it comes to committing to a relationship.(nothing to do with Luthor, just her bad experiences and controll needs.)
Which Luthor realizes So what does he do? He kicks away the foundations that Lois life revolves around, her work, suddenly she is forced to re-examine her priorities and discovers that the world outside the Daily Planet is a scary place but luckily Luthor is there for her, offering her succour, and of course she naturally gravitates to him.
Now the Lois from season one isn't a nice person, but I think the viewers and most certainly Clark realizes her bitchiness stems from fear and not some inhererent evilness. Her work colleagues OTOH probably finds her very difficult.
In comparision, in the comic the “man of steel” you have this exchange:
Give me a chance and I could make you the happiest woman in the world.
By making me wife number seven or is it eight? You do tend to make Henry VIII look like choirboy.
Is that it then Lois? you reject me because I’ve been unlucky in love? It’s quite obviously a different Luthor and it’s quite easy to see why there are no chemistry there. My impression is that the comic book Lois is also far less complex then the Lois in the series, Comic book Lois have a stable relationship with her family, no bad break ups, doesn’t simply project the bravado, she is spunky through and through. This Lois has no real need to be confirmed, hence Luthor has less attraction.
That is another reason I love L&C because Shea play the perfect psychopath, showing Lois attention affection and concern and gives he space as a hyper-intelligent charismatic multi-billionaire should if he had taken an interest in her.
To see what I mean, imagine that one of today's most famous persons had tried to live a double life in such a way that even his "other identity" was seen in public.
It is kind of silly. But I remember a fic that gave good explanation for this:
Lois is beating herself up for not seeing the obvious and Martha or was it Jonathan? tells her a story about a farmer they knew that looked exactly like Clark Gable with mustache and everything. Everyone who meet him marveled at the resemblance, yet despite that, no one misstook him for Clark Gable, because Clark Gable wasn't dressed as a farmer or plowed fields in Kansas.
