I review Avenger based on its demo. It's quite easy to install it, though has more than 4Gig factory content, but it's OK for me. One word from the the developer : Vengeance Sound means quality, and browsing the forums I have never read any bad about their stuff.
The factory sounds are good, but for me, something is missing (maybe I should demo it more). Similar hybrid monster synths like Zebra or Blue II contain more presets I like. I think my problem with the sound is that VSP Avenger mainly offers sounds for the todays' producer, and don't contain "oldschool" sounds in its factory set, Sure it can sound many different ways.
Anyway, the GUI is interesting with lots of visual feedback and animation, so a great fun factor, but on the other hand is quite a mess. There are some parts that are small despite of their role, for example the modulation matrix should be bigger% from the whole gui. I think Avenger gui problem is that they want to put many things in one screen, where some parts should deserve a second screen alone.
I Quite like the Arpeggiator, and the Zone screen where you can layer sounds. I only tried some of the effects, and filters. That was really interesting to see a "tape stop" kind of fx in the effects rack.
So currently I have mixed feelings with Avenger. The main reason of this is I mainly like synths that are made for one specific goal, and Avenger is not this kind. It is made for covering many synthesis types, and the question is if it can sound wicked enough...