Its seems after its release on PC, the forums were preoccupied with massive threads of grief, due to the many problems people were experiencing. I, for one, still use the 32-bit client, and am not going to 64 until it's stable and linked to launcher.
BUT . . . Took a sick day from work yesterday, and felt well enough to work through initial quests with my brother, and we had a blast - sneaking through the no trespassing areas, watching my brother get accosted by the guards while I hid in the shadows snickering, infiltrating the mansions of the rich, and the general mayhem that comes with the life of a thief! My brother mentioned that he thought that this was the best DLC yet, and I think I'm leaning in that direction, also.
I know that many problems persist, particularly with the lag in Cyrodiil, but the game played flawlessly as we worked through this content.
I do have one message for the devs: Take your time with the upcoming Dark Brotherhood even if it misses the deadline of the 2nd quarter. Don't release with problems that would smother the excellent content that is inherently there.