The word that best defines new D&D 4 products is purpose. D&D 3.x can be seen as a test of sorts by Wizards of the Coast. They learned what worked and what didn't and most importantly, learned how customers used their products. Gone is the cynical design strategy of throwing in just enough content to make both groups, players and DMs, compelled to reluctantly buy every product. I think this new strategy has the added benefit of lessening piracy, despite recent claims by WOTC. Talking to customers, they had a tendency to feel less likely to buy a product and more likely to pirate it, if the usable content for them was minuscule. Make a solid product overall and people will want to possess it.
The new strategy has every product designed for maximum use, for the group it was designed for, backed up by online content and tools. For example, dungeon tiles were a rather worthless product in D&D 3.5. You had these random 1-inch square tiles that didn't relate to anything. The new Dungeon Delve book uses these tiles as the maps for the encounters, with all of the monsters integrated into the online tools. Suddenly the tiles are in high demand and I'm stocking them wider and deeper, and lamenting their limited production runs. I'm personally hording them for future use on my own bookshelf, in quantities of at least two. Books designed around a topic, like dragons or undead, have new monsters, new encounters, and suggestions on how to run campaigns with these new additions. Online content appears in the database a few weeks after the book release.
As for the books themselves, there's a clear distinction between player books and DM books, rather than creating hybrid books that only marginally satisfied each group. This means that a DM book is tightly designed for use, with practical examples, pre-made encounters, and usable content rather than flowery "fluff". In fact, if I had a complaint about these books, it's that there is rarely enough fluff. These are not books you read for pleasure (a sizable chunk of RPG purchases), they are tools. Even information on monsters is displayed in a "knowledge check" format. Useful, practical, but it feels a bit sterile sometimes. Books focus on crunch, but DMs books still have chapters with practical design ideas. This practicality has sold me and where I would only occasionally buy a DMs book in 3.x, I've found myself very pleasantly surprised with all the 4e DM books.
For example, I've got a campaign about to start in which I've liberally used Draconomicon, including one of the encounters and a new dragon (heavily modified using the online Monster Builder tool). I've dropped in one of the Dungeon Delve adventures as a side plot. Open Grave provided many of the higher level monsters along with design ideas for cultists. Also don't forget digital content. A 20th level stand-alone Dungeon magazine adventure (in PDF) provided the framework for a 7th level adventure of my own design. You can't beat a good map and all the maps and graphics are available online.
You can't discuss DM content without mentioning the new digital content. The tools are clunky, but useful. My new method for making an encounter is to reference the DMs guide Encounter Templates section. I'll then choose the type of template that I want, such as Battlefield Control, or Dragon's Den models. I have a tendency to use a lot of solos and elites, a holdover from previous editions, so I need to learn to add more monsters and different encounter types.
Once I know the type of encounter I want, I'll wade through the Monster Manual, Open Grave, Draconomicon and Forgotten Realms Campaign Setting for things that catch my eye. If I have no idea, I can open the DDI Compendium tool and search by level, role, race or any monster criteria. Then I can use the Encounter Builder tool to whip up an appropriate challenge. The content of these electronic tools are then dumped into Microsoft Word and easily converted to a table for in-game reference. Artwork and maps are likewise dumped into Word, facilitated by WOTC being far more digital friendly in 4E.
So what does this mean for the store? First, book sales are clearly delineated between players and DMs. While 3.x books sold a mish-mash of books to both groups, many of whom grumbled about usable content, 4e players happily skip DM books and are far more likely to buy player books. Player books are a store bonanza, selling 2-3 times as many as a 3.x book. DM books sell far fewer copies than before, but to much happier customers. Sales are also far spikier, like what we find with Games Workshop products. What does this mean? People come in and buy their books on or close to the release date in droves. It's harder to regulate inventory, but it's rewarding when you get it right.
Spiky sales means good company communication. Customers know of a release and its date because Wizards of the Coast has successfully transmitted that information. I think this is also a by-product of the D&D Insider service, which tells you on the sidebar of current and upcoming products. That's not new, but how many people hung out on the WOTC site before 4e? I'll also point out that the usefulness of the digital tools in no way precludes the need for print products. It's a fine line, for sure, and I use a lot of digital content for products I don't care about (RPGA adventures have fantastic scaled monsters). However, I'm very happy to have the print product to reference when I make a digital selection.
So what don't I like? The Dungeon Master's Guide errors are so astronomically bad as to necessitate some sort of special re-print. This is the book I originally hinted at as being irrelevant, yet I now use it extensively as a template for traps and skill challenges. The DCs are all off and the errata only goes half way. In general, anything with a DC in the DMG can't be trusted. Traps and Skill Challenges should be in the Compendium tool. That would go a long way towards fixing the DMG problems. It's the only content that I need that is not available in digital format.
There are few dog products in D&D 4, the truly bad ones are the special editions. These are the core books at $75 with gilded edges and with the first generation of errata. Someone forgot to pleather bound them. Big mistake. The digital tools are still clunky, but getting better. I don't know if I'm a normative user, meaning my method of using them are typical, but I would like to see the tools better formatted and integrated into how I use them. For example, my copy and paste routine should be less work. An actual encounter design tool that does what I do in Word would be ideal. That would be a full solution rather than a suite of tools. A link to a graphic of the monster would be helpful too and perhaps a real link to the RPGA adventure when that has been referenced, rather than the RPGA home page. Overall it's a great start. Remember, 4e has been out less than a year.