In most of its register the bassoon is capable of the most sensitive lyricism and for this it has been exploited by many composers.
Some composers have not only written music for the haunting upper reaches of the bassoon, but have also exploited the lower registers, such as the low A required by Nielsen in his Wind Quintet. Most bassoon music is written in the bass clef, but for the upper registers bassoon-players frequently have to read the tenor clef.
Gareth Twigg talks about the range of the bassoon and what you have to learn when starting to play the instrument.