Walls streaking

It looks like this wall was not properly primed before it was painted. The paint job is showing what is usually called flashing: delineated areas of the surface where the texture or appearance does not match the surrounding paint.

It appears you have a medium gloss paint. Unfortunately, gloss amplifies every little imperfection in the underlying surface and can make for some really nasty flashing. Larger walls, bright lighting (ie. sunlight), and very sharp lighting angles will make it even more noticeable.

It's a bit harder to say what is actually causing it. Some change in texture and composition from the rest of the underlying wall surface is causing the paint above it to dry differently (this is what primer will prevent, by sealing the old and creating a fresh, homogenous surface for the new paint).

My guess is that it's some drywall compound that was not adequately covered after the walls were finished. If that stuff gets applied at different thicknesses (which always happens, it is unavoidable), it acts like a sponge when any kind of water based paint gets applied over the top, sucking out the moisture and creating areas that dry differently. This can happen even after several layers of paint.

The best way to fix it would be to get a good oil based primer and go over the whole wall with at least one, and preferably two even coats. You must use oil based primer, so also plan for good ventilation and probably a respirator and goggles. Once the primer is dry, repaint in the same color and it should look a whole lot better. Most primer is white when you grab it off the shelf, but the store should be able to tint it closer to the top coat color so you won't need as many coats.