As mentioned, nodes really give one the power that would be impossible to do with menus. Sometimes the (node) flow seems rather vague though. I have always approached learning logically and node networks seem a perfect fit. With World Machine, I can work a classic left to right and wind up with everything linked to an end output(s).
A new user of TG2 is likely to get confused, especially if he/she is the type who wants to know why things work like they do. For example, I look at the default TG2 scene and see Terrain connected to the Shaders connected to Objects (Planet 01). That makes sense. Then the Atmosphere connects to Planet 01. Okay, I'll add a lake. Wait, the Water group has the Water shader 01 and the Lake 01, and Lake 01 has an output, but it's not connected to anything. But its there when I render.
So suddenly I have doubts I understand the way the TG2 node network works and I can't approach it "logically" (or at least my logic.) Is there a default connection to all devices that have outputs (that gets used if it's not connected?) No, because some when disconnected work like they do when disabled.
For me, if there was a final group called "Scene" with all the other nodes connecting to it, it would make everything "clearer". But maybe that's just me.
Please don't take this as a complaint about TG2. I'm just throwing out my thoughts on the subject of node networks.