Some of my most valuable playtesters are my kids, because I can watch them play, and see things that they do that they might not report if I wasn't sitting there. I was watching my daughter (age 11) play today, and she is _terrible_!
I mean, she isn't actually terrible. She can move around, and attack the right enemies, and so forth. But she is not a power-gamer by any means, and misses a lot of the subtleties that, in designing the game, I assume the player will take advantage. For example, she keeps getting ambushed by assassins, who sneak around and kill her spellcaster. This very spellcaster has a spell "See Invisible", that lasts for an hour, and would be very effective against these enemies. But, I don't think she even knows that the spell exists. And I despair, if she didn't have the spellcaster, that she would figure out that she needs to go and buy a scroll and read it to learn the spell, etc, etc.
This leads to a couple of problems. She ends up with her party getting wiped out pretty often, but TotAW is pretty forgiving of that. The party gets resurrected, and she goes back and tries again, and hasn't really gotten stuck yet. Still I can definitely see the potential for frustration here.
There is a more subtle problem, too. She also ends up buying a bazillion healing potions. Not all at once, but she ends up relying on consumables (specifically healing potions) a lot more than I expect. This uses up most of the gold she gets, and then she can't afford to upgrade her equipment. Which in turn makes the game a bit harder.
I've got thoughts on what to do about this, but I'll leave that for a future entry. For now, I will just say that the experience of live playtesting has proven illuminating.