As a D&D newb, would a barbarian/druid have too much overlap to be worth not going pure druid? I have very fond memories of my half-orc barbarian7/druid13 in neverwinter nights but not sure if it would be feasible in actual D&D.
Not a single point of overlap, really. The problem would be from the opposite direction. Two bits:
1. MAD, or Multiple Attribute Deficiency, or "Reason #4 Why Monks Suck". A barbarian needs Strength and Constitution, and ideally Dexterity, to be good. A druid needs Wisdom to be good (and things like Constitution and Charisma don't hurt). That is three attributes to keep buffed, compared to 1-2 for most single-class characters.
2. Under-leveledness, which doesn't have a good casual term. If you do that same build, your 20th-level druid will be several levels behind his druidic peers, as well as dozens of hit points behind his barbaric peers. He will be worse at everything, and it is (usually) better to be able to do one thing well than several things poorly..