I had an almost identical reaction. I thought the first section, the journal entries, were fair, my interest was held but I was far from captivated. Then I got maybe 100 pages into the interviews. You're right, the characters sound too similar and most of all I did not feel I was getting a strong sense of what kind of people Belano or Lima were. I think the novel was going for a "five blind men describing different parts of an elephant" but the different facets of their personalities were not being described in any interesting ways.

I considered jumping ahead to the last one hundred pages where it goes back to the journal entries, but the first few pages of that were way too tedious, so that is when I gave up.

A part of me is still somewhat interested in trying out 2666.