I'm glad to see Heroscape is still alive and well. It is a system that has loads of potential and continues to have a strong fan following at Heroscapers.com. It's only natural since Wizards of the Coast was given control over the Heroscape brand that they should attempt to draw more attention to DnD with the release of this new "master" set. The 3 stars I give to the set are mainly only against its value, at least at its street price. It certainly could have used more terrain and a wider assortment of figures.
This set's strongest points are the new dungeon, shadow, and rock outcrop tiles, along with the new figures. The dungeon tiles provide a new look but offer no special rules on their own - some figures may gain a benefit from dungeon tiles depending on the description of their powers. The shadow tiles provide defense and can boost some figures whose powers specifically require shadow tiles. The figures consist of four adventurer style figures (fighter, rogue, wizard, cleric) along with some squad and unique villain figures (drow elves, a drow boss, troll and black dragon). The powers of the figures are very reminiscient of 4e DnD powers, which function well within the Heroscape universe. The figure types mostly feel like their DnD counterparts (the cleric heals, the rogue can flank, the troll regenerates, etc.)
The sample scenarios at the back of the rulebook are of a different style than the scenarios in other Heroscape rulebooks. The DnD scenarios act very much like a room to room dungeon crawl rather than a single long term battlefield. The new methodology behind these scenarios doesn't actually require this DnD master set to make use of it (anyone could have come up with it and applied it to other Heroscape sets), but it offers an interesting spin on how to play Heroscape more like DnD.
You don't get nearly as much terrain or figures with this set as you do the other master sets (Rise of the Valkyrie and Swarm of the Marro), but fortunately the street price of this set is less. I would say, however, that for the price, you get less in this set than the others (half as much terrain - only 2 24-hex pieces along with a multitude of smaller pieces - and less than half of the figures of RotV). Rise of the Valkyrie is still king when it comes to the first Heroscape set you should acquire, especially if you can find it for a discounted price. And where Swarm of the Marro only felt like a few heroes fighting a Marro encounter, the DnD master set is exactly that - four heroes fighting villains. You can of course add the figures to the rest of your Heroscape collection, since they are compatible with the rest of Heroscape.
The only reason to pick up more than one of this set is to get more dungeon, shadow and rock tiles, or to get more of the figures to add to your collection. If you like the new tiles and want more of them, you'll certainly want more than one of this set, given the small amount of terrain you get with it.
If you're only curious about how to play Heroscape more like DnD, then you can probably get your hands on the sample scenarios somehow without purchasing this set. (Also, check out www.playdnd.com for a PDF download of some Heroscape scenarios for this set).
In only a few short months (March 2010), a new Heroscape small expansion with 20 new figures geared towards DnD will be released.