Clarinets are very flexible and quite easy to learn in comparison to other instruments. In terms of music, it can play just about anything that the clarinetist will learn. This instrument has the versatility to convey softer, relaxing sounds one minute and the next sound strong, intimidating, and almost aggressive.
Aside from the 'typical' Bb clarinet--the one that most people learn on--there are also the bass clarinet, the A clarinet, the Eb clarinet, the contrabass clarinet, and a few others. If you learn one clarinet, you will be able to adapt easily to the others and can possibly learn other, more challenging instruments like the oboe.