Zendesk is a pretty powerful CRM, which is generally pretty easy to administer and meet the needs of a Support organization (the field of my experience is administering it). It's built on a robust set of APIs, but can be administered purely through the GUI in almost all cases. Review collected by and hosted on G2.com.

Zendesk can be slow to improve new features or products, like their Messaging product which has many gaps that have not been closed since its release. Additionally, many parts of the GUI are frustrating to work with. An example, when building triggers and using tags as conditions, the tag titles are truncated and unreadable. The Explore product is not good. Review collected by and hosted on G2.com.