I kind of go back and forth about them. I love that they kick started the budget synth movement, but at the same time I wasn't remotely inspired by their original line finding them to be solid for standard sounds, but really lacking in features that make them stand out from a sound design perspective. Essentially, when it came to making music on a budget I found these to be significantly less inspiring than most of my VSTs coupled with a cheap MIDI controller, particularly with Volca's like Sample which was a pretty big misfire for me. Even when thinking of it in terms of mobile production, they are hard to justify when more full featured portables like Novation's Circuit exist or simply owning an iPad with some simple apps. Plus, I'm not an analog purist at all, so it's main selling point of cheap analog didn't really hold an appeal for me. There are some people doing really cool things with them, but they weren't quite my speed. Not hating though, if you love them keep doing what you love.
However, this changed with the Volca FM, which really provides something unique at its price point. It sounds lovely. The complicated nature of FM synthesis is simplified and I think it is the first module hitting the full potential of what this line can be. I'm also pretty interested in the upcoming Volca Drum and Volca Modular which seem to have an amazing set of features on them and provide something new to the market.
I'm pretty appreciative of the ground that the Volca series broke and I'm fully aware that they will have a legacy that lasts. Much like the Microkorg was the entry way for a whole generation into hardware, Volca is going to be the gear that kick starts a whole generation into music making simply because of affordability. Much respect and I'm very interested where they go into the future.
I loved the OG 3. Never touched the kick/sample. Fm was sick. =)