2K Boston's Ken "She Looked 18 to Me" Levine sent in a clarification about his earlier comments regarding the plot has to be really f***ing stupid for people to keep up with it post.
"I talked about how the very basic plot of your game has to be very, very simple so people who are not inclined to care about your story can follow it. In BioShock it's
Act 1: Get to the sub
Act 2: Kill X
Act 3: Kill Y [edited out the names in case you haven't played it yet]
However, once people are attached to those primal threads, they can, IF THEY CHOOSE, go deeper."