Version 1.5.2 specifically was a "minor update" that squashed some critical crashes from 1.5.1, but mostly, it served as the stable bedrock for servers to thrive on for nearly a year before the World Colour update (1.6) arrived.
To understand why the 1.5.2 community remains so fiercely loyal, you have to look at the blocky details. minecraft 1.5.2 online