I think Operator is great. So lightweight and powerful. A big part of that is its usability. I'd rather use it over other synths outside of Live, but little feature gaps keep turning me away.
Things that would kick ass (some of which could be hidden away from the novice on an 'Expert' screen ala FM8):
* a fully-featured, unified mod matrix. There's currently bits of this on the LFO panel, the Filter panel, and the Pitch panel, but they're not as flexible as many would like (you can't route them to any part of the synth, only a few), and they're on seperate 'screens'. This would give Operator the power of a more fully modular synth, without losing its simplicity. Eg: route LFO to osc AMP, not just pitch. You currently have to go to fiddly lengths to get this effect happening. A _full_ mod matrix, involving all the powerful features of Operator, would really open this synth up for creativity.
* pulse width modulation wave type - this seems strange to be missing in the first place
* waveform symmetry ala Reaktor's Soundschool analogue subtractive synth. This is so simple but gives you huge power over saw up, down, triangle etc
* four oscs, why not four LFOs? Dave Smith's Evolver is fantastic because of this. Operator could do it so easily!
* osc syncing for various parameters
* expand the chap so it can do wavetable! Multi-point envelopes! Step sequenced goodness. There's no reason why Operator can't chew on 'massive' synths that hog enormous CPU resources, and still keep it's tiny, simple, usable interface.
* Edit: input. Lots of modern synths can take it. Why not Operator
* built in hidden micro-game of tetris, seeing as the algorithms suggest this already. As in uTorrent. Minimal file-size increase...
I'm writing all this because using Operator is so much fun, and I think it could be even more fun! I've got tons of friends interested in it, from DJs to engineers. Creating the most lightweight able-bodied synth ever is a great goal.