Ungh, Cyanogenmod is a beautiful thing. Hangouts is...not the shit...there isn't a single video utility that I'm really happy with, though Firefox just released a chat service which I'm looking forward to trying out. As for Nova: The main reason you'd want it is if you want the ability to customize everything. Plus it's pretty damn fast. But I can control the way just about everything looks on my phone, and what gestures do what, and it gives me a lot of options for organization. Haven't used Google Now, so I can't really compare the two.
Google Now is basically "swipe left for Big Brother." It will helpfully give you search results for that search you did while logged into google from your computer earlier in the day that told you all you needed to know. It will also give you the weather of that place you were in for three weeks but haven't been back to since September. What was kind of hilarious was the bugs. At one point I looked up "Superbowl" to see what time it was playing. For a month it gave me "Superbowl" headlines that were, in fact, about Suge Knight.