First the price is absolutely too high for what you get. Everything cost extra in terms of licensing and some basic functions demands extra modules to work. The functionality is not much better than Solidworks or Inventor but cost many times more.
The performance is poor and large assemblies tends to be very slow and sluggish to work with. Back in the 90's NX was known for being one of the best in terms of large assemblies but is has not developed at all since then. Multi-core CPU's and GPU cores are not utilized well and the waiting time for updating models ans drawings can be very time consuming. The Parasolid core shows it's age and belongs to another decade than more modern design software that handles advanced lightning and material surfaces much better and faster.
In general the software is stable but there are some irritating bugs here and there that you have to be aware of for every release. Siemens are not fast on fixing these and send out service packs. Sometimes the only solution is to buy "the next version" for a lot of money. Siemens really know how to make money from customers.
The compatibility to other softwares are quite poor if they are not compatible with the Parasolid core. It heavily relies on old formats such as STEP and IGES. JT format is OK but exporting and importing is time consuming not without problems. The choice of formats to import from other "Automative" softwares such as Creo or Catia is rather poor. If you work in other business NX is not very good in compatibility. Review collected by and hosted on G2.com.