I'm curious to know what you didn't like with Nova and what Apex does better?
Well with Nova I kept having the issue with Folders getting removed from my home screen or apps being removed from the folders (Something Apex fixed a while ago but Nova haven't yet). Also If I closed certain Touchwiz features like the Stock RAM manager and other Stock items it would revert back to Touchwiz - I know I only have to press the home button again but its not the point.
Also with Apex the screen transition effects are just so much smoother and better looking - such as the Cube effect - looks more 3D - also there are more transition effects than on Nova. I also don't have the any of the issues I mentioned above with Nova - but i'm only a few days in to it.
Also it has Notification add on for counts and Widget locker works just as well as it did with Nova.
the only 2 things I don't like about Apex is when you pinch out to add another home screen page like you do on the stock or Nova all you can do is preview - to add a home screen you need to go to Apex settings and can be annoying. The other thing is you can only do one back up at a time.
Other than that the stability in my opinion is better so far.