I learned my Astrology from modern authors and then gave it up becauseof other pressures. When I returned to it, some 30 years later, the reawakening of interest in traditional methods was getting into full swing. I must admit to being predisposed towards it but it was sometime before I actually began reading traditioonal texts. When I read Lilly's description of the signs, I found something totally alien from my early studies. Indeed it's such a culture shock to read traditional texts that the full import takes years to sink in. So Dave is right, Astrology can be overwhelming!
Dave mentions the tripartite model of planets, signs and houses. I think the main difference between the 'sun sign' approach and the traditional approach (and some modern approaches) is that when I learned Astrology, these three were treated as almost coequal (and not necessarily closely related). The traditional approach sees the planets as what matters and their sign and house positions simply provide specific information on their status in a particular chart. Signs and houses are both very subordinate to planets, they simply help to set the planets in a specific context and enable their specific roles to be interpreted.
I'm still trying to get to grips with the traditional approach, so I can understand the difficulty newbies have with Astrology but I can glimpse a coherent system which is geared not to telling people more about what makes them tick but is geared to telling people more about what is going to happen to them and when. This is not a deterministic standpoint, Lilly knew 250 years before Leo that a person's social class and family background meant people with similar charts would develop in different ways. Neither Lilly nor Morin put their forecasts in modern probabilistic terms but it's clear that both saw probability (or God) could lead to variations in outcomes.
Read Lilly or Morin and you will see that neither is a 'fortune teller' - the (wrongful) accusation made against Astrologers in the nineteenth century and against Leo in particular. It's a 'scientific' approach (in their terms) and it's that which makes it so fascinating.