Despite having a draft of a playtest document already, they claim that they want input from gamers on what Type V should be like. Well, here are mine:
Did I order a kitchen sink?
Why, no. No I didn't.
If you're going to put out a game that you want people to actually play, you need to redefine your concept of "core rules". I don't want three vast tomes that I have to fully read and digest before I can start to play. I want to get started and learn more from there.
Start us off with one core book, why don't you? You can call it a "basic set" if you like, but before you do take a look at the old basic sets for what they did right (and the older WOTC ones to see what NOT to do...). Actually, take a look at the Pathfinder Basic Box for a not-too-bad idea.
Give us 4 classes: Fighting-Men, Clerics, Magic-Users and Thieves (yes, I know you're going to change the names. That doesn't matter. The basics do matter, though, and you know that you know this.) You want your fighter to be different? Roleplay it! You don't need five different fighting classes.
Give us 3 or 4 races. Just humans, elves and dwarves would work (okay, halflings if you absolutely must...). We really don't need to start out with half-Tiefling, half-Dragonborn, fully psychotic unplayable messes. Really we don't.
But players like lots of options!!! you say.
Bloody good for them, then. You want us to have options? Fine, put out option books. But make it absolutely plain, both in the player's and DM's sections, that options are OPTIONAL. Nobody can come into my game and insist that idiotic class/race combination is automatically playable because "it said so in this book!". And while we're on that subject:
Empower the DM.
It's his or her game, after all. I got quite sick and tired of 3.5, because there were far too many books and the players would use them to slap the DM around. He wouldn't take it, but they kept trying. Hey, I'm here to game, not to watch another argument. If you could just put in the book somewhere, in nice bold print:
it would certainly save a lot of grief. (Your mileage may vary; it's possible I've just been playing with a bunch of immature mooks for the past 30 years...)
Bring back the sense of wonder.
If you absolutely have to put in a system for every hick redneck magical type to make their own magical items, put it in a supplement. An entirely optional supplement.
Magic is supposed to be ... well, magical. The production line, magic-as-tech version from 3.5 (and I'd assume 4.0 as well) was entirely wrong for D&D.
"Hey, we found a wand! Let's see what spell it duplicates."
Whatever happened to the Wand of Wonder? That was a nifty item. And it's a good example of how magic should be, truly wondrous and not just another 'ho-hum let's toss it on the pile with the rest of them' kind of thing.
(There should also be a section in the DM's advice on keeping magic rare. In one game I was in, we seriously considered making for our house a picket fence out of the innumerable +1 swords we kept picking up...)
What else? You might want to mention in there that it's a game of exploration, not combat. That changes the whole emphasis and thus the whole game (and for the better, I think; again, YMMV.)
Also, take out critical hits. Gary Gygax warned DMs not to include them, no matter how much the players wanted them. Sure, it's kinda cool to deal out an incredible amount of damage to the bad guy, but when he does it to you (and far more often...) it's not that much fun.
And it's about having fun, isn't it? Or is it just about selling more product?
Anyway, that's the view from my branch of the tree. As Craig Ferguson says, "I look forward to your letters."