The general rule of thumb should be: What got YOU hooked on the series? Doubtful it was the non-existing prequel you picked up, ;)

Maybe you just need to explain to them that New Spring was more of a prequel to the series AFTER quite a few books were out already? It's sad to see a potential reader not liking the series.

In my opinion, New Spring was kinda child-like and not really RJ's style. Child-like in the sense that it throws a bunch of stuff at the reader and doesn't explain them: As such, it takes away from the depth that is truly RJ's style and makes it seem that the One Power is just ye ol' magic. Don't get me wrong: I think it was great to get some background on Moraine/Lan, but I think it should have been labeled more of a side-story then a prequel.