The auto-completion is so phenomenal in IntelliJ, you'll be tempted to learn Java just to use it. Yes, that's fairly hyperbolic, but after using IntelliJ, I just can't ever go back to Eclipse or any other Java IDE.
The ability to edit programs while they were running and then see the changes nearly instantaneously after saving without restarting the program was fantastic. (Worked just as well as Eclipse's after a few tweaks.)
What I'm really looking forward to is what they do with C/C++ and possibly Go some day.
IntelliJ is worth every penny if you write Java code; don't doubt it for a moment. Download the trial and use it if you find that hard to believe.