Well you didnt waste money on AP since you cant play CW without it, it`s expansion. And you`r right CW is extended campaign in form of new quests, units, skills, abilities, items and such. It same world and islands as in original campaign of AP but this changes add allot in gameplay and possible combination of builds/units . . .
It also have 2 smaller campaigns which are stand alone and can be played as such, but main change is CW campaign itself and it`s bonus to original campaign as i mentioned.
As you said , you already read some things here on forum so you`ll get well with this game. Have fun
