Linux is developed under the GNU General Public License and its source code is freely available to everyone. This however, doesn't mean that Linux and it's assorted distributions are free. Companies and developers may charge money for it as long as the source code remains available.
Linux does not come in only one package. Many distributions are available. I recommend trying out S.u.S.E., RedHat or Debian. Slackware is also well known by veterans.
Linux is pretty stable as a workstation and as a server machine. Multitasking functions very nicely also.
Hardware support is assured by volunteers, and sometimes companies, all over the world helping the Linux cause. I have found Linux hardware support to be very good.
As a Unix clone, Linux boots by default to a text mode screen which makes is very suitable for low end servers. Its Unix heritage also makes it a true multi-user system with full access security as well as integrated remote login.
You can't have more control over the operating system than this one. Modify the code that gives you trouble and recompile!
XFree86, the GUI of Linux, is not part of the operating system, but only a program that writes to the screen. As such, when the GUI crashes, it can be easily restarted. No need to reboot to gain back access to the system. XFree86 can also change resolution on the fly like Windows NT, although all X Windows applications need to be closed to change color depth.
As with any Unix operating system,TCP/IP Network support is all there and doesn't need any add-ons. Every bit of utility or application needed to run TCP/IP all comes freely with the operating system.
XFree86, the only GUI server available in Linux, runs over the TCP/IP stack. Such a design cannot bring high performance and real-time graphics to Linux.
No real good GUI environment shell exists for Linux yet. KDE currently comes the nearest as a decent shell, but it's still a bunch of bugs in development. GNOME offers more potential as its goal is an application interface which will allow applications to work together, since current X Windows programs don't. Most of them cannot even share the clipboard. This makes Linux unsuitable as a workstation OS.
Sound card support in Linux is still pretty cloudy. There are no Multimedia Control Interface at all in Linux.
Even with great distributions like S.u.S.E., Linux remains very user unfriendly. A lot of manual setup needs to be done for about anything you can think about from mounting a diskette to installing a font. No easy help is available, unless you find the answers in the HOW-TO files.
Linux does have stability, security and performance issues running as a server. Other Unix such as FreeBSD, OpenBSD and Solaris exist that do a better job as servers.