You DO have the power of the BSD command line.
I work from the command line (choice of all the usual shells) a lot, right on the desktop. There's a "Terminal" application standard, and a full "X11" application package for running xterms and other programs like OpenOffice which use X11.
There's no requirement that you use the GUI except at login, and if you are logging in remotely using SSh, you don't even need the GUI for login.
It's a full, largely-standard BSD Unix. The only stuff that's a little different are functions like user accounts, which are managed from OS-X level rather than the old standbys like /etc/passwd.
Cool. Thanks.