[dragonwriter]

> While sci-fi addresses intellectual concepts well, often its other elements are weak. This applies especially to characters, who frequently are no more than walking, talking representatives of those concepts.

When that happens, its often intentional -- that is, the characters exist as vehicles to explore the interplay of the concepts as such, and are not intended to be anything else. Its an approach with a fairly long history (thousands of years) in writing.

OTOH, there's lots of scifi that isn't like that, either intentionally or accidentally.