Regarding zbx_module_init() documentation says:

If successful, it should return ZBX_MODULE_OK. Otherwise, it should return ZBX_MODULE_FAIL.

If module initialization fails Zabbix prints only module name:

		zabbix_log(LOG_LEVEL_CRIT, "cannot initialize module \"%s\"", name);

Would be nice to let modules return anything but ZBX_MODULE_OK in case they feel like it. Would be nice to print this error code in Zabbix log file. This way module developers and users would have a way to diagnose module failures without the need to implement their own logging or hack Zabbix'es logging functions.