Something Wicked adds a lot to the game. I enjoyed the base game but it just didn't feel complete but adding Something Wicked makes the game feel right (even when not using both boards). I frequently feel this way about Flying Frog games -- the first game is good but something is missing or doesn't just work right which is added by the first expansion. Frequently just more cards seems to be the majority of the fix.
I also feel that the game works best if you take all the recommended optional rules as being rules that should be always used. The tweaking of the rules in the Something Wicked manual does seem to fix a few problems in the base game. I also really like the Cult of the Crimson Hand being added to the plot of the game.
sounds awesome to be honest. Also as an Arkham player from beginning i thought i needed more meat on the bone so to speak. Cannot wait for this box!