I like boxed sets, especially for the "starter set." The entry point to the game can be a single product, but still have separate player and DM books, as well as dice and any other appropriate accessories.
I don't think that the "starter set" needs to be a separate product. I still have a fondness for the BECMI approach of adding options and complexity as you gain experience with the game, and the Basic Set never became obsolete.
I've never been involved in a campaign that went on long enough to get past 10th level in 25 years of gaming, and I suspect I'm not the only one who has never (or only very occasionally) had use for the higher level content. The inclusion of character options for progressing through to level 20 (or 30 in 4E) is a major reason for the huge pagecount of the core rulebooks, and it's a major accessibility issue for new players.
There was also something cool about buying the next set when your characters were ready for it and discovering what new horizons were available to your character, versus seeing it all laid out in the book when you first created your character. Yeah, this might be just me, and it's an experience that you can only really have once, but it was very cool.
To use 4E terms, if the rules were to be released in boxed sets for Heroic (1-10), Paragon (11-20), and Epic (21-30) tiers, then you could have more streamlined books that didn't have 100+ pages of spells or powers. If the players were more interested in a "low-magic" or "gritty" campaign, then nobody needs to purchase anything beyond the Heroic rules, and there is a natural stopping point to the campaign.
I really like the Essentials DM's Kit, with a DM's guide, counters, poster maps, DM's Screen, and a sizable adventure all included. It would be a great way to get started as a DM.
The Essentials Monster Vault was also a great product, with all of the counters, the maps, and an adventure in addition to the monster book. I love the idea of including all of the appropriate monster tokens with a monster book, although if 5E is moving away from using minis and a battle grid in the core rules, it isn't as big an issue.
I also think back to older boxed sets, such as campaign settings, that would often include two books, four poster-size maps, transparent grid overlays, and a stack of full-page "cards" that had adventure ideas, player handouts, compiled tables, and other visual aids (such as gods' holy symbols). I love all of that stuff, and hardcovers make it very difficult to include such items.
I predict...
...a Player's Handbook, covering the first two complexity dials and core races and classes (160 pages, $20 loss leader for the first year, upped to $25 after)
...an Advanced Player's Handbook, covering the second two complexity dials and more races but hopefully not classes
(200 pages, $30)
...an Essential Monster Manual to begin with (120 critters on 120 pages, $20)
...a Monster Compendium Annual (I'd *really* love to see a return of the binder system - I'd be prepared to pay a premium price for that format; however, it will likely be just 300 pages, $40)
...a Dungeon Master's Kit (Screen, Guide, Dice) (cardboard screen, 120 pages, 7 dice, $30)
...a Forgotten Realms Campaign Boxed Set (Old Grey Box II, three books with a total of about 400 pages, poster map, premium quality materials, $60)
These two posts deserve XP!
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This thread makes me consider the following...
A D&D Heroic Boxed Set that gives you four races (Dwarf, Elf, Halfling, Human) and four classes (Cleric, Fighter, Rogue, Wizard). The box is for levels 1 to 10, of course. It has the frame work of the D&D game with none of the 3e or 4e designs. No feats, prestige classes, or advanced grid combat rules. There are Vancian spellcasting for the cleric and wizard and "stunts" for the fighter and rogue. There are optional skill rules and a variant spellcasting system based on either spell points or 4E's system.
The box includes enough of the rules and monsters for low-level campaign arc. It comes with either a new module or an updated version of one of the classic B/X modules. Or maybe one of each. An homage to an original and a new sequel module that takes the classic adventure in an entirely different direction.
After this box comes the core rules, the PHB, the DMG, and the MM. This would be the core game that builds on the framework of the Heroic Box. The PHB includes not only the races and classes from the box but the other iconic races and classes from the 1e, 2e, and 3e PHBs minus a class like the monk, which should be saved for an Oriental Adventures hardcover.
In truth, perhaps the sub-classes should become themes instead, so you would have one theme for each of the following: assassin, bard, druid, ranger, sorcerer, etc. This makes themes work a lot like the old 2e kits but with a better design. It would include a more complex skill system including the 4E skill challenges mechanic as well as rules for adding feats, as per 3e/4e. The DMG would give you everything you need to create your own additions to the core rules.
The three core rulebooks are for levels 1-20, but it includes an appendix that details taking the game beyond the Paragon tier.
As an alternative, their could just be one core "rulebook." It would be a Rules Cyclopedia for D&D Next. You'd still have a Monster Manual or perhaps a boxed Monster Vault. You'd support this tier with a trilogy of adventures.
After the core rules have been out a while, you release an advanced rulebook (or an advanced PHB) that looks at tactical combat and anything else that complicates the game to the point that it needs to be looked at in detail.
This also might be best if done as a boxed set. Sort of an D&D Advanced Tactics Box. This book/set details levels 1-30 in all its full advanced glory. This would be the ruleset for people who love the grid combat system of 3e and 4e. It would give more character options. Instead of paragon paths and epic destinies, you'd have advanced themes. These themes would be tied directly to grid-based combat. Think of this as the heir to the old BattleSystems rules but built off of the best design concepts of 3E/4E. It would come with counters and its own trilogy of tactical adventures.
There would also be an Epic Tier book, as a separate product that would build upon the classic D&D roleplaying concepts for high-level play (levels 21 to 30). Sort of an Advanced Dungeon Master's Guide. It would work with the Advanced Tactics Box, but the two products wouldn't require each other. It would have it own themes devoted to role-playing instead of roll playing. This book would be supported by its own adventure trilogy as well.
(I'd also like to see an Immortals Handbook that looks at adventuring after level 30, but I won't go into that here.)