This is basically it. The great balls have a higher chance to catch (actually it seems they just lower the color level from Red to yellow or yellow to green, etc), they are succeptible to seemingly random curves. This is negated completely if you throw a curve yourself.
If I am using great balls, or if the monster is higher CP and I am just using regular balls, I always curve now. If you turn your phone diagonally, and make like a Nike Swoosh type motion, it gets really easy to use. I'm guessing as you get higher player level, this is going to be mandatory, so it's probably better to practice on junk pokemon instead of getting assblasted by that 900CP Charizard that you want so bad but can't hit.
It's a really annoying mechanic though. I'm glad the game director (or something like that) said that one of the things they want to do is explain the mechanics better. I still am not 100% convinced that throwing when the inner circle is smallest is the best way to catch something. Also, I'm still confused about what causes a "nice" or "great" or "excellent" throw. Excellent gets you 100 extra xp per catch, so I would totally be trying to do it if I knew how.