The Blingdenstone adventure that is packaged with the DnD Next playtest is quite good, conceptually speaking. It's sandbox-y, providing 6 short adventures that can be accomplished in any order, with a combination of combat, dungeon-crawl, exploration and role-playing. There are also a number of places to add extra adventure hooks that can allow things to spin off into a larger campaign - which is what I may do if it holds our interest.
That being said, there are a number of weak points, too. The maps in particular are lacking, notably the Town Center map in adventure 3. The overall cavern map is pretty sparse, too - but it fits with the sandbox ethos in that it lets you develop quite a few of the details as you see fit. The encounter and tunnel maps are a nice shout-out (well, copied from, to be honest) to the old blue maps - these ones come from Vault of the Drow, I think.
The adventure has quite a bit of material in it, and the organization isn't that great. The occupied sections of the ruins aren't presented first, but are interspersed with other caverns, and random encounters for specific caverns are only detailed in their entries, which are all scattered in the first 5 or 6 pages of the module, so the first thing I did to make it easier to run was write myself out a couple of reference pages. These will allow me to track events in Blingdenstone more easily and keep me from having to constantly flip through the adventure to reference things. Having this kind of cheat sheet is essential to running a sandbox, I find - if only because it allows me to respond almost instantly to things the group wants to do.
Ultimately, I put together 3 reference sheets.
Blingdenstone Summary Sheet
The orc summary is basically just compiled information from the adventure - crib notes, essentially, where I can track how many have been killed and look them up.
The Gnome and Blingdenstone Summary are a bit more interesting. The whole idea behind this adventure is the reclamation and rebuilding of Blingdenstone, so what I wanted to do was set up a system where the gnomish position, and the gnomes themselves, get stronger as the different adventures are completed, or get weaker if the characters dawdle too much, fail to complete adventures or certain random events happen.
The main thing here is stats for individual gnomes, because curiously enough, other than the stats for the guide to the Wormwrithings in Adventure 2, there are no stats provided for the gnomes anywhere in the module. In some cases, the gnomes can be expected to fight alongside the PC's (such as when orc raiders attack the barricades), so having stats for them is important. I'm also tracking the number of healthy/injured gnomes in Blingdenstone, the same way I'm tracking the number of orcs.
As you can see from the sheet, successfully completing some adventures causes additional gnomes to arrive, or the gnomes to get better equipment or more HP and morale. This is a bit more bookkeeping, but it makes the impact of the party more obvious and concrete. I'll also stat out the major NPC's for use in the events, but for the moment, I'll treat them like normal gnomes.
I also added a couple of cool things to the summary - enlarged Blingdenstone and Underdark encounter tables and a random major event table which can alter things in the city in a major way.
Other things I'm doing that I'll detail more later:
Stat out the major NPC's.
Rework the Wormwrithings (Chapter 2) encounters to reduce repetition.
Add more adventure hooks to Mantol-Derith (Chapter 6)
Reduce XP values of monsters substantially (20% of current, approx)
Rework the pregens, add a couple of new ones.
Enemy activity page for the drow chick.
Update Town Center Map for digital tools.
Modify Journal notes to make them more interesting.
Add Cult of Urlden adventure hooks
Change encounters in Chapter 3 (more zombies, more skeletons, wight from drow to gnome king).