Intellij IDEA is very easy to use, and has great developer aids. The autocomplete for methods/variables is very useful. If you have the full version rather than the community edition then there are great things to help with server side development too.
It works well with GIT (and other source control systems), which makes team work simpler.
The code completion bits are very handy, for example just typing iter will give you the relevant "for loop" and even suggest what you want to iterate around.
The integration with Maven and Gradle is also good, and I use maven for my server based projects, and have used Gradle for Android projects, though I now use Android Studio, which is based on Intellij.
There are lots of features that I haven't had a chance to use, but the ones that I do use are excellent.
The change of the pricing mechanism from one where you purchased it outright, and then could upgrade to a license system where you pay an annual amount is not good, and has stopped me upgrading. I also personally find the introduction of various Java extras, e.g. Scala, Groovy, Kotlin has taken the aim away from the core Java development, though I realise that it may be useful for others.