I've tried 3 cameras: the V1 (5mpix), V2 (8mpix) and a wide-angle (5mpix). I've had trouble with exposure with all of them.
One small gripe: the raspistill command --help arg lists a zillion options without a clue about what the default values are.
But that's not my story. I want to take snaps from before dawn till after dusk and I found that the many exposure-related arguments seemed to be ineffective. But I finally discovered the silver bullet. Shutter speed (-ss microseconds). That one works.
So, I average B/W pixel values in python and adjust shutter speed accordingly. My current -ss range is (bright to dark) 500 to 4000000 microseconds (1/2000th to 4 seconds).