Prior to The Stranger Camus received a BA in philosophy, an MA in Christian Thought and wrote a number of non-fiction pieces. This was his first work of fiction and...I think it reads like that, as a philosophical idea with characters and plot built around it. I enjoyed it because I like literature that makes me think but if the idea was "life has no meaning so how should we proceed" I think he might have done better with a protagonist that tried even a teeny bit to find some meaning. In the same way, I don't believe the protagonist's "epiphany" at the end of the story that he had 'been happy' and that he would have realized that earlier if only he had opened his heart to "the indifference of the universe". Huh? 
 First of all, this was not a happy man. In fact, the dullness of his interactions throughout the first half of the book made me think maybe he was mildly depressed. He takes buses, he smokes cigarettes, he views the landscape and carries on short conversations but never does he engage in a way that an even mildly happy person might engage with the people around him. He sees his mother's "fiancee" have a fainting fit but offers no help. When a good friend of his mother's cries at the funeral, he says "I wanted her to stop crying, but dared not speak to her". Yet what a surprise when later accused of callousness! Is it really the universe that is indifferent or is it indifferent people that make it seem that way? 
 Throughout the first half, also, the protagonist claims that things "have no importance". He could marry Marie or not, he could accept his employer's offer to move to Paris or not. "I didn't care much one way or the other" he says because "one life was as good as another". Does this sound like a happy person? Does this sound like the universe being indifferent? Or does it sound like the kind of B.S. a moody teenager might spout. 
 This phrase (near the end) got me too: "...supposing she were dead, her memory would mean nothing; I couldn't feel interest in a dead girl". This just confirms that all the protagonist feels are physical sensations: the desire to touch Marie, the heat of the sun or the coolness of the evenings. If death only means the cessation of physical sensation then - sure - the protagonist is right that who cares if death occurs at 40 or 80, by guillotine or by old age? It's all the same. Yet most people's lives have motive, a reason for doing something that creates value to our lives that the protagonist neither has nor understands. (The word motive sprang to mind when mulling over Mersualt's crime since he, predictably, has none). 
 Sorry - if you shoot someone 4 times at close range and then feel "less regret than a kind of vexation", I will have to argue that you've either got a psychological problem or you are a creation of a philosopher's active imagination.