I tried some different products for network monitoring since the top dog Nagios is everything else but easy to maintain.
Tested products were:
Configurable by XML files, so suffers the same problem as Nagios - you need something to configure it comfortably or spend time writing the config yourself. Compatible to Nagios plugins.
Really great interface. Supports Nagios plugins. Easy addition of own plugins. For me, this one had the best feature set.
Not really intuitive configuration. Supports Nagios plugins, offers own extension system (ZenPacks).