I just started playing the Nethergate demo, and I must say, I'm impressed. My portable is a G4 iBook, so my Mac gaming options are pretty limited, and I'm thrilled to find a company developing great RPGs for OSX with modest hardware requirements.
However, given that Avernum and Nethergate use the same (or at least a very similar) engine, and A4 supposedly has a bigger storyline, I'm unsure as to which I should spend my money on. I like replayability in RPGs, and neither game's info page mentions anything about 3rd party campaigns or other features to ensure replayability.
So, to put my question bluntly: does Nethergate get boring once you've beaten both stories? I know people do higher difficulties, Singleton, etc. to make the game harder, but is that all there is? From the demo, it seems to be a linear plot with optional side quests; once you've beaten the plot and all the side quests, what's left to do? Is there enough variety in later-game character development that playing through with a different party would be substantially different?
Also, on a related note, how long are the two storylines? Are we talking 100+ hours of gameplay before this becomes an issue, or am I going to be out of storyline to play through a week after starting?