Clear, Distinct, Deliberate
The way Meursault sees the world is kind of like a scientist looking under a microscope: the scientist doesn't look for the beauty or the allusions in the mold or microbes that she's checking out, but you better believe she sees everything.
Frivolous language is absent, but Camus' descriptions are meticulous. With this painstaking attention to detail, we get everything from the roundness of Marie's breasts to the contours of the evening sky:
Soon after that, the sky grew dark and I thought we were in for a summer storm. Gradually, though, it cleared up again. But the passing clouds had left a hint of rain hanging over the street, which made it look darker. I sat there for a long time and watched the sky. (1.2.8-10)
The sentences are clipped, and the is vocabulary simple. At times, it even seems childlike, but there are also moments of profound clarity and expressiveness—and it can be really pretty ("a hint of rain hanging over the street" is nice). But it's also almost clinically detached... like Meursault himself.