They are indespensible. Here are my comments:
[b]Pitch[/b]
This is indespensible because without it, one would not be able to adjust the note spacing/zero beat position.
[b]Volume[/b]
This adjusts the sensitivity of the volume loop. I use different settings depending on the music. For very expressive playing, I prefer a larger distance (a la Masami Takeuchi). For some of my looping works (which require rapid attacks), I prefer a compressed distance (greater sensitivity).
[b]Brightness[/b]
This is very important -- I often vary the brightness from one situation to another -- even for the same compositions. In general, I prefer a little more brightness in a larger space.
[b]Waveshape[/b]
The exact wave form isn't as important as having contrasting waveforms. In general, I find sine, square (or triangle), and bright (sawtooth or pulse waves) useful. Subtlety of timbre is less important to me than the availability of contrasting timbres. I very much like the Epro's approach that includes a useful set of preset timbres and a user-settable position.
Having said this, my theremin compositions have been written specifically for the Epro. This includes the use of contrasting timbres (my latest looping compositions utilize contrasting timbres and will be included on my not yet released cd). The use of presets make the changes much faster and less stressful in live performance situations. Unlike some synthesizers that I have seen over the years, the Epro's factory presets are quite useful. Bob really knew what he was doing when he developed those presets.
I value a clear, sine-wave tone. Not that I use it all the time, however I want access to that sound.
A big issue for me is linearity, since my music demands specific notes (pitches) -- even my original music. Bear in mind that a linear theremin with limited timbral variety will be more useful to me than a non-linear theremin with lots of "bells and whistles".
How linear is "good enough"? I would suggest that a theremin builder strive for something at least as linear as an Etherwave Standard and strive to acheive the linearity of the Ethervox.
I don't want too much, huh? :)
[b]New theremins[/b]
I am excited at the prospect of new, highly playable (linear) theremins and look forward to playing and/or acquiring them.
[i]--Kevin[/i]