let's just say it is difficult.
for some reason adobe thought it would be great if AS was a real programing language instead of a scripting language.
some of the basics i know are, it is partially interperited and extreamly dynamic.
it uses byte code (like java), extreamly object oreinted, more low level of control than previous versions,
XML can be injected, it uses a new VM for AS3 only, it is ~12X faster than AS2. it supports REGULAR EXPRESIONS (yatta) thats RegEx for some of you, run time exceptions too YAY(you mean it will tell me i have a problem?!),
all in all it looks powerful but is radicaly different to the point that i don't know how to start... so be back soon ish,