I tried to play a theremin once. I sounded awful, like the soundtrack to "The Day the Earth Stood Still" had caught fire and crash-landed into the Bermuda Triangle. It's easy to get noise out of a Theremin, but hard to make great music with one. Famed synthesizer brand Moog has a solution designed to ease the instrument's learning curve.
The Theremini is a theremin with pitch correction. You can choose a scale and root note and let the machine help keep you in tune as you flail your hands about. You can also set the range, choosing the highest and lowest notes. It comes with a headphone jack so you can learn the instrument without annoying anyone within hearing range.
The process is further helped along with a built-in tuner to guide you in learning pitch and scales. Pretty soon, you should be in shape to compose your own sci-fi soundtrack. I would recommend re-scoring the entire "Star Trek" canon as an exercise.
The theremin has been challenging musicians since it was patented by Leon Theremin in 1928. The Theremini could help a lot of new players join the fold. The pitch correction can be set high (think T-Pain levels) or turned off completely once you have mastered your hand positions.
Moog had a prototype of the Theremini out on display at the National Association of Music Merchants show. It will come with a $319 price tag when it's finally available. Moog is currently accepting preorder inquiries.