One of (if not) the best NMS platform out there. And if it wasn't enough it's also open-source. Simply awesome. Thanks guys from Zabbix SIA and the entire community for this great project.
Not suitable for large infrastructure (painfully slow with 10k hosts), web interface is inconsistent (ex: column sorting not always possible) and browsing experience is uneasy (ex: switching from data to configuration without keeping host context), unsecure (any host can pretend being another). The macro system and rules look like nice features but are plagued with numerous bugs, some unresolved for a long time. Should not be used outside domestic testing.