What do you like best about Ubiquiti Network Management System?
The visual interface is quite intuitive, and data can be sorted in a variety of ways, including through built-in metrics and regular reports on aspects of network operation which the small-scale or less experienced user wouldn't even know to ask for.
Adoption and provisioning (automatic configuration to work in your network) of new devices like UniFi security cameras, security gateways, Wi-Fi access points, and UniFi phones is a snap, making implementation of network expansions and integration of new equipment simple and easy.
A daily scan of the network console, from a web browser or a mobile device app, keeps you on top of your network health, and premium support plans are available for those who need product experts to be immediately available.  If you have experienced and knowledgable staff, you can avoid the additional support costs. Review collected by and hosted on G2.com.
What do you dislike about Ubiquiti Network Management System?
If you're accustomed to more fine-grained management systems, like those with popular command-line interfaces for configuration, you might find that some of the features that you expect to have available to you aren't immediately accessible through the GUI.  SSH access is required to get to these options, using standard Linux command line tools, with the full array of configuration options.
Hot, automatic network failover between gateway and router devices is not yet ready for prime time, but is being worked on.  If you need this to function without human intervention, it's not there yet.
Support is available through forum posts only, and is quite sparse, unless you pay for the premium support package.  Although the user community on the forums is quite knowledgable and helpful, the best support doesn't come without a cost.
Be aware that this system works only with Ubiquiti's own UniFi branded equipment, and while devices from other manufacturers can be seen in the list of network endpoints, they can't be managed (aside from DHCP reservation).  Even Ubiquiti's UISP and Edge Router lines cannot be managed by this system, so be sure that anything you buy (https://store.ui.com) is compatible.
If you didn't purchase your equipment DIRECTLY through the UniFi store, you won't get warranty RMA support from the company, and will have to go back to the vendor from which you purchased the hardware for any replacements.  Bear this in mind when shopping.  Many devices are chronically sold out, and come back into stock infrequently and for very short periods of time.  Get on the email alert list for these if you need them and aren't willing to pay scalper-level prices (often up to double) for them. Review collected by and hosted on G2.com.