For "Madness at Gardmore Abbey" to come out just before the dreaded reveal of the new edition in the works is bad, because a lot of people will begin holding their money or trying to get the books on PDF torrents instead of purchasing this box. And what a huge mistake that would be. Because this is a fine product, probably the best 4e story so far.
Your players can start from several very good adventure hooks, even linking the super adventure with previous quality works such as "Reavers of Harkenwold", which leaves room for the DM to flesh the plot with ideas of his own. But right away they bump into the new storyline regarding the Abbey and the secret which brought the garrison to an end: a powerful artifact of Chaos, which is woven into the story in such a subtle way you don't feel it as a "commercial" plotline. Moreover, there are quite a few open villains, hordes of monsters and even "neutral" rivals -a different party of adventurers, described with their own personalities and moral definitions, no less!-; yet the main drama comes from the misterious Secret Collector, who can happen to be someone your characters know from a long time -specially if you ran "Keep on the Shadowfell"-, someone they respect or someone who has a goal of family love. It does not matter: in the end, the Secret Collector has become corrupted by the Deck of Many Things, the aforementioned artifact.
Plus, the end of the adventure may deliver either great treasure or doom for a player character. If it is the latter, then the whole party is on the verge of a new adventure. Why? Because if players gather the whole Deck, its true magic is released and a person can make a draw. Depending on the random card drawn, the character can gain riches or disappear, prisoner somewhere far, far away. In the meantime, before the Deck is fully assembled, each card has a lesser power which can be used during encounters.
On the technical side, the box has good stuff inside. Books are printed in quality paper, maps are great -although, as usual, too few, but hey, Wizards has to make money from Dungeon Tiles and the like-. Tokens are not as good as in the Monster Vaults but they do. The Deck of Many Things, however, features wonderful artwork, and the two included treasure cards are certain to inspire lust in your players.
Monsters and encounters are well planned, and you get to have companions, such as an orc fighter or an eladrin maiden warrior -with whom I've fallen in love with, much to the chagrin of my wife-. Certain villains will want to make an alliance with your players, while others will strike on sight.
Roleplaying is a MUST. It's up to the DM to get players to like or hate the NPC's and get into their character skins. Moral choices are to be made. This is 4e at its best, so get it. And gather your players ASAP.