It'll be available to Insiders April 1st for $359.99 USD. It comes with 3745 pieces and 5 minifigures. For more information, check out their press release.
Even for those who aren't DnD fans (Like myself), this is still an awesome set. A bit pricey perhaps, but a great looking model, and a unique looking castle set.
Never played, D&D is only familiar to me through 80's animated series. The set looks good and has plenty of good bricks, but there's no chance I'll have it anytime soon, if ever. Time will tell.