I have two of Warlocks in my fridge. They taste exactly like Pumking with a little bit of roastiness. You really think Pumking tastes like water? That seems crazy to me, it's 8.6%. To me it tastes lighter than traditional pumpkin beers insomuch as it doesn't have overbearing spice notes and has a nice graham crackery finish. But it doesn't taste like water.
Also, I don't find Warlock to be very "stout". It seems much closer to a brown ale. I definitely would not put it in even my top 20 stouts, though it isn't terrible.