Save Versus Death has published the first of his Saturday Night Delves with an incredibly vicious dungeon: The Return of the Iron Lich. Let me tell you, for starters, this is way more than any mere delve. It comprises several keyed locations, which feature nefarious tricks and traps, haunting images, and terrifying monsters. Oh, and as the heroes progress through the dungeon (IF they progress!), we learn more and more about the history of the eponymous Iron Lich. Holy moly Batman, there's actually a story hidden in this adventure!
I'm not going to give away any details of this adveture except this: you get exactly 4 hours of table time to complete it. If the 4 hours are up and the Iron Lich is still floating around, the PCs die.
Needless to say, this module is not for newbs. Any DM running it had better know it backwards and forwards and have an excellent understanding of the 4th Edition game mechanics. If your group typically gets bogged down in single combat scenarios for an hour or so, you don't have a chance. But if you have a group that's looking for a truly unique challenge, this monster of a dungeon is for you!
Seriously, WotC, take notice. This is the way that truly challenging 4th Edition Dungeons and Dragons adventures should be written. If I were running things there, Sersa, the guy behind Save Versus Death, would have a very good-paying job.