This is still the only Multi-player First Person Shooter (MMFPS) out there besides WWII Online. A damn nice one to.
As of Summer 2006 there is still an incredible player base allowing you to jump right in and have fun any time of day, any day of the week. In addition, if you don't want to spend the cash, Sony has the Planetside Reserves allowing anyone to play for free. While the free players are not able to master as many weapons and vehicles, they still contribute an enormous amount to the gameplay.
If you have been out a while or have never tried it, come on in and join the fu.