Rated 5 out of 5 stars

It is an excellent add-on, but in the new version (0.17) you have to push the ctrl with the mouse wheel for zoom. In ver. 0.16 using the mouse wheel was enough for the zoom.

I prefer the older method, so I had to downgrade back to ver. 0.16.
I understand that many people prefer the newer method instead.
It would be great to put a checkbox in the option about it (or at least an about:config variable), so everybody could chose the preferred method.

This review is for a previous version of the add-on (0.17). 

From version 0.17 onward, the default zooming control has changed to be consistent with firefox's built-in one.
As such, you now has to do ctrl+wheel to zoom (this is the same command used on webpages) and wheel to scroll vertically: this is meant to ease new users that may be used to the standard command.
You have therefore to choose: you can use the new command (rest assured that no-one better than me knows how painful it is: I originally coded this extension for myself and I've been using it with the old control for years!) or go in about:config and set extensions.imagetweak.legacyscrolling to true (this is explained in detail in the online help http://cafxx.strayorange.com/ImageTweak%20Help).
Hope this fixes it for you.