Hmm... well it depends.
Music software in Linux is not latest and newest, but to say it is like using software in DOS is a bit exaggerated.
I use a Linux workstation at one location and Sonar (and windows) on another location.
The software I use most (there is a lot more) is:
Ardour:
http://ardour.org/ Rosegarden:
http://www.rosegardenmusic.com/ Muse:
http://www.muse-sequencer.org/ And for music notation Musescore:
http://musescore.org/ As plugins I use the native Linux plugins, but also a lot of Windows plugins (using Wine and WineASIO).
The fun of Linux is you can use the window manager you like. Personally I use KDE on Debian, but you are free to use what you like. And do not forget Linux is also 64 bit, so you can utilize your full memory..
Anyway - Linux is very well usable. Although the platform is relatively small (in numbers) it has good support by their users (and developers).