Molly is actually a fairly interesting and complex character if you follow her from Johnny Mnenmonic all the way through Neuromancer (especially the second half) and Mona Lisa Overdrive.

It's tempting to write off Case's behavior as just a realistic portrayal of a washed up addict, but thematically there's a strong and likely intentional parallel between the way he's coming apart and the way one of the main AIs in the story is coming apart. If you add in Linda Lee and the other AI, what Gibson was trying to do becomes a lot clearer. I'm intentionally being vague to avoid spoilers.