My favourite synth. Period. Very versatile. Has a GREAT sound. Do you want it fat? I can hear you. Do you want it agressive? Oh yes, I can hear you. You want it smooth as silk/cream? One of the easiest things. Check out the 400 FANTASTIC presets. World class.
User interface: Well, I don't like the scrollwheel approach too much but I got used to it. Looks nice though.
Sound: Did I already say that this synth sounds absolutely awesome? Wanna replace e.g. your JP8000 with a VSTi? No problem with this one.
Features: Man, it can do a lot. 6 OSCis, 2 Filters with 10 different characteristics that sound great, 6 LFOs, 8 Envelopes, tons of FX, etc., etc.
Documentation. Good and nearly complete.
Presets: Awesome. Usable.
Customer support: One of the best in the whole world.
Value for the money: Compared to the (few) other top notch VSTis this synth is at the lower end of the price range. Worth every cent.
Stability: Didn't crash once. Super stable.
If you think that VSTis are toys: Check out this one and prepare to get shocked. One of the best shocks around. ;-)
Revisited this oldie today. 5 instances, ~45 polyphony, all 2x oversampled = 30% CPU usage, which includes all insert effects. They don't make synths like this anymore. One instance of Diva alone reaches 50% at high polyphony.
It's not really fair to compare this to Diva. They use different ways to make sound. Z3ta is a wave table synth and Diva is a virtual analog synth that what I think recreates the circuits of an old analog synthesizer. That takes a lot more processing power. Also you can change the quality in Diva. But I agree with you. Z3ta is an awesome synth.