Yeah, FM and RM are good but it be nice if there was more modulation modes such as amplitude modulation and phase modulation, among others.
I think the current FM is actually PM…
Phase and Amp are possible with the keytracked LFO’s (real FM as well).
Also, Matt said he’s working on more modes for version 1.1
RM at 50% is the same as amplitude modulation. But as exm said you can also use keytracked LFOs for this since the Level values modulate at audio rate. Some people like amplitude modulating the sample this way.
If you like the audio rate mod stuff you could also try modulating the filter cutoff with a key tracked LFO. Can get a lot of sounds with higher resonance on the filter and a bit of modulation from a sine LFO.
If you like the spectral warp modes on the left knob though I’ve got some more in the works.