These are my own DDXP/5E experiences, with some commentary on 4E.
I just returned from DDXP.
ObBackground: I started with Holmes & 1E over 20 years ago and like a free-form BASIC best. My wife likes 3E best and started in the 2E era.
The play-tests were NDA and I'm not playing Paper & Paychecks in order to be killed by an Ancient Red WOTC. I was reasonably happy, but then again my session was run by a VERY good DM. He made 4E Ravenloft fun last year and he made the play-test game fun. A good DM transcends game systems, however I don't think he had to work very hard. It's hard to judge an early draft of a game system, hence the 'reasonably happy' statement. I played D&D and I liked it and enjoyed myself. My wife played D&D and liked it and enjoyed herself.
The real test of 5E will come with the rules modules/subsystems. This portion was not included in the play test to my knowledge, so I'm going to talk freely about it, given what they've said about it at the seminars and my own thinking in the last few days.
The rest of this post has NOTHING to do with 5e. This is NOT a *nudge* *nudge* *wink* *wink* statement.
I'm pretty sure that Supplement 1: Greyhawk, was just a booklet of optional rules. The same for Unearthed Arcana? Most versions have a statement to the effect of: if you don't like something then throw it out, or change it. And yet … we don't? Oh, we house-rule the crap out of certain sections, but there's a tendency to use what's presented in the books as the gospel. "I don't like skills so I don't like 3E." Then don't use the skills, geez! Wanna play OD&D? Remove all classes except the Fighter, Wizard, and Cleric and get rid of skills and feats. Bang! OD&D. Want a more variable combat system? Allow the defender to roll a d20 and add his bonuses instead of taking 10 on his defense every time. Want group init? Then do it. We all house-rule the rule like crazy, and yet we complain endlessly about The Rules. 5E will be successful, in my eyes, if they can present the CORE of the game and then everything else as options. For example:
Combat Option 1: d20+bonus vs defenders d20+bonuses.
Combat Option 2: d20+bonuses vs defender "Take 10"+bonuses.
Combat Option 3: "Take 10"+bonuses vs defender d20+bonuses.
All 3 have different flavors. Option 2 is OD&D. Option 1 is more swingy. Option 3 might be more cinematic.
Group init or individual init. (with the advice that group speeds play and individual is more tactical.) Maybe group the options, so there's a 'tactical' set and a "fast play" set, and a "cinematic" set.
If they can design a game that FINALLY gets the gamer community to drop and house-rule, as a way of life, then they may be able to accomplish their goal of unifying everyone under "one" set of rules.
The public play-test got me thinking a lot about game design, and I finally 'got' 4E. It makes sense as a natural evolution of D&D and I stopped hating it. It just should have never been released. I'd like to talk about 2 mechanics in 4E: the At-will, Encounter, Daily and the STAT vs DEFENSE combat mechanic.
At Will, Encounters and Dailies have always been in D&D. Your at-will was an attack, swinging your sword or some such. A thief may have had an encounter power, like backstab, and Vancian spells can certainly be thought of as a daily. What 4E did was to recognize what the earlier versions of D&D were doing and codify that. Now backstab was explicitly listed as an encounter. No ambiguity as to when you could use it.
A sword blow was always (ok, AMOST always) STR vs AC. Missile were DEX vs AC. Feats in 3E made melee attacks DEX vs AC. Spells in 3E sometimes attacked FORT, or REF. If we stretch we can also say that earlier version included this mechanic: dwarves get better FORT bonuses in 1e … err, I mean poison saves. 4E recognized what was already naturally going on and simply codified it. It took the ambiguity out with the result being a much cleaner rule system. Both of these represent a natural evolution of the D&D system, evolving from idiosyncratic mechanisms (d6 init, low AC/THAC0, % thief skills and d6 open door rolls) in to a core system that makes sense in 3E and 4E. No more multiple die types for many rolls, just a d20+ bonus … and you could take 10 on many of those rolls.
For example: a martial attack is d20+bonus vs AC. AC is 10+ bonuses. In essence, you take 10 on a defense roll all the time. For spells in 3E the attacker set the DC by adding a bonus to 10, with the defender making a save by rolling a d20+bonus. This was the exact opposite of how a martial attack worked, but both are really a sub-case of a single rule: you roll a d20+bonus and try to roll higher than a d20+bonus. In some cases you can take 10 on the roll. That's amazing and I can't believe I just now picked up on it.
I have a hard time believing ANY player of ANY version of D&D, from OD&D to 4E can take exception with those two mechanics, and their evolution. The 'Breath Weapon' saves and descending AC might be treasured from a nostalgia standpoint but I can't see how anyone could defend them as specifically supporting a certain play style, unless it was the OBFUSCATING style. (But, I am willing to listen to you if you can articulate it.)
In other thoughts: 4E gimped the exploration element of the game by removing resource management as a game play element. Exploration always has a timer attached. Wandering monsters. Lair reinforcements and new traps. Etc. By removing a timed element you gimp the Cause & effect play of explorations. Your actions no longer have consequences if you don't have to worry about resources. This is why tracking light and food is so important, as if the healing rate and wandering monster checks. The longer you spend in a dungeon the greater the chance you're gonna die from a wandering monster, or your light will run out, or so on.
All in all, I think 4E made at least one critical sin and maybe two or three. First: it put the game design RIGHT IN YOUR FACE. DAILY. ENCOUNTER. AT WILL. SURGE. STR VS DEX. INT vs WILL. This is something that only an SPI game designer could love. It looked like board game rules. The fluff surrounding the rules were terrible, or just ignored completely. This overly regimented rule system extended to the character sheets, where you had page after page of powers, poorly laid out, with mountains of text for eve the most simple of things. This slavish devotion to form and the 4E writers style guide turned the game in to "hunt for the power" instead of Doing Cool Things. This horrible layout & rules style was reinforced by the official products. Modules & Encounters had the same mechanistic layout and style. It was hammered in that this was the right way to play the game. And people left this over-powered mechanistic version for the OSR, or Pathfinder.
This concludes my random thoughts on game design theory and modularity.