Z3TA+

User Interface:

I quite like the way everything is laid out, especially in version 2.0, where the new GUI is larger, easier to read, and has a far better visual representation of what you are actually doing. At first, Z3ta can be intimidating to use, but with some practice, you'll "get" it pretty quickly, then programming new sounds becomes a piece of cake.
The Modulation Matrix behaves differently than in most synths, and that is the part that takes some getting used to. For example, in order to route the modulation wheel to close filter 1, it's not as simple as simply slapping "Modwheel" as the source, and "filter 1 cutoff" as the destination, then entering a negative value in the range slot. You have to put "ON" as the source, set "Filter 1 Cutoff" as destination like you normally would, THEN...you have to select a negative curve under the CURVE slot, select "Modwheel" under the CONTROL slot, then finally enter a POSITIVE value in the RANGE slot. Whew!! Man, oh man...when I first got Z3ta, I was tearing my hair out in frustration just trying to figure that out! The thing is, with added complexity like this comes added power. You can adjust the curve in how that filter modulation behaves. Select "Slow -" in the CURVE slot and then when you move the modwheel, the filter will close in a logarithmic fashion instead of a linear one.

Sound:

It ain't an Access Virus and it ain't Sylenth. It's Z3ta. It has it's own sound to it and I definitely like it very much. You can run the entire range from warm and analog all the way up to brittle, cold and digital. However you program it, with enough dedication to learning its features, you should be able to nail whatever sound you're looking for with at least 95% accuracy. Pay particular attention to the filter buses to get those lush, wide stereo sounds. Hell, let's take it further: with that and 6 oscillators, who needs a chorus effect? Combine the filter buses, some LFO action on the pitch on a couple of the osc's, maybe some light LFO on filter panning, and you made your own chorus effect. Sounds great on pads. Definitely try it and see if that works for you. Synths like Z3ta and Zebra really have quite a bit of leeway in defining their sound because they have a sufficiently high number of adjustable parameters that you can "bend" it well beyond the type of sound that jumps out at you on first impression.
Having said all that, I've seen synths with much more analog sounding filters. The digital character of Z3ta's filters become evident when you crank the resonance up. Then again, there's definitely some use out there for that character and I'm not complaining.

Features:

When it comes to the Z3ta vs Sylenth debate, THIS is why I pick Z3ta any day. Everytime. I'm a "mad scientist" when it comes to synths and that means I like being awash in a bunch of parameters just sitting there begging to be tweaked. 6 LFOs and 8, that's right, EIGHT envelopes can be assigned to quite an impressive list of parameter destinations. The number of LFO shapes on offer are simply astounding. Same goes for the oscillator waveshapes, and OMG, I love this -- the waveshaper parameters -- which can be tweaked on EACH oscillator separately. In Z3ta 2, you can also modulate these shaper parameters via the matrix and THAT is pretty cool :). Z3ta has those onboard effects like reverb, chorus, phaser, flanger, distortion, delay, etc, and...."meh". I like the delays and distortions, but the modulated effects and the reverb I'm not wild about, personally.
There are some features still missing in Z3ta 2, though. If Cakewalk adds new features in a future update, my wish list is as follows:

-Ability to modulate Evelope Attack and Decay values in the matrix.
-Ability to modulate Delay time and feedback in the matrix.
-An "Alternate" or "Flip Flop" source in the matrix.
-Ability to set the Decimator BEFORE the filter. As it is now, I don't use it much.

Documentation

They give you a PDF file that explains Z3ta's ins and outs pretty thoroughly, going over every single parameter and what it does.

Presets

They're good tutorial material for gaining an intuitive understanding of Z3ta's somewhat unusual mod matrix. From a musician's standpoint, there are a lot of them and IMHO, many of them are quite good, expecially the new ones in Z3ta 2. Check out the ones by Frank Genus ("FG"), BigTone ("BT"), and whoever "BC" is.

Customer Support:

At their very heart, I believe the folks at Cakewalk are good people who want to make their customer's happy. In my personal dealings with them, they always replied PROMPTLY to any questions I had. Example: I had trouble downloading Z3ta 2 at the Cakewalk store, sent a message and BAM!, they were on it right away. In regard to Z3ta 2's bugs and all the talk about that, I know as a business owner myself that there are many not-publicly-known variables behind the scenes at work which make it harder to get what you want done as quickly as you would like, as thoroghly as you would like.

VFM:

I got Z3ta+ during the $20 sale. It's easily woth more than the full price even as old as it is. There's a reason it's a classic and so many people swear by it.

Stability:

Z3ta+ - 10/10
Z3ta 2 - 5/10...currently buggy, but I'm confident they'll fix it.Read Review