Kubik is a modestly complex wavetable-type synth. I'm not going to go deeply into the technical details because (a) it's already been covered and (b) I'm not a tech-head, I just want to play!
The UI is nice, easy on the eyes, and everything is easy to get to. Bank loading/saving and preset selection are fairly common-sense, although how a preset is saved with the song but not the bank last loaded threw me off for a bit - a post in the ConcreteFX forum and I had my answer quickly. You can't beat getting a fast answer from the person that developed the synth himself!
On to the most important thing for me, the sound. Kubik can make the most amazing noises! I've stacked two/three instances and had some killer pads, which is mostly what I use Kubik for. There are a ton of presets, both that ship with Kubik and many others freely downloadable, so (being the preset user I am) I have a pretty large pallette to work with. It can be a bit harsh at times, it's definitely digital, but I like that (lol). The factory banks are nice but don't show the full power of the synth, I recommend Tim Conrardys banks as well as the Blaster and DJSL banks.
An excellent value for money, I'm actually surprised there isn't more buzz about this synth! It's not an end-all/be-all instrument but it does what it does quite well! :-)