none of the classes (and this is initial reaction, only) really offer the thematic qualities to make me want to role play them. Also the bonuses never seem to outweigh their penalties.
In BG2, which used kits with penalties and bonuses in a similar fashion, I can always build a concept for a character, and know that functionally that class can work. A swashbuckler/mage in elven chain mail, a fighter/shadowdancer-- the gain and loss for taking these combos is very clear, and it changes how you would play the character--what role they take in the party, how they function in combat.
Here, (and again at first pass), the sub-classes feel very restrictive. They take away more than they add.
Some of them have interesting ideas behind them:
the drug-monk works for me conceptually
Ghost Heart is an excellent idea.
wizard and priest are functional i guess, but there doesn't seem to be much creative about it.
maybe for people who really theorycraft, there is some good synergy behind the choices, but for me-- who just wants an interesting concept, i can't say there is much to recommend them.
I'm sure that opinion will change though.