This is disappointing news. One of the most disappointing aspects of the news is the damaging speculation it has already begun to cause (evident in this thread, for example).
I thought Cook had some great ideas, just off the top of my had the advancement of race from Arcana Evolved and the high magic mega city of Ptolus.
I think his influence was an important to come up with an edition attractive to the widest possible fan base. Like others I don't think the damage is definitive. But the perception caused by his leaving will be damaging in itself. Which is a real pity. I just want for D&D to do well. And I would love for them to achieve their goal of coming up with a version that could unite the very fractured fan base. This won't help what is already a monumentally difficult goal.
That said I do have a few comments I'd like to share.
Cook will have already have had a major influence on the design. His leaving won't take away from the work he has already put in. True, his influence will not be there as things move forth, but, surely he has had a big influence up until now. And if the first playtest has been announced for May, how different can what they will offer us be from what it was yesterday before Cook announced he was leaving?
Also, if we take Cook's mention of the possibility of future consultation as true and not politeness, perhaps he will still have some influence on an aspect of the game yet.
[sblock=Rant]
Secondly, what is the story with the term 4venger? Is this being used as a blanket term for fans of 4e? If so, it's use is not only inaccurate but I, as a 4e fan, feel mildly annoyed at being lumped in with those that have commented they are glad Cook is leaving. For a start I'm pretty sure some of the people who have commented that they don't like Cook's work are not 4e fans either. I am a 4e fan and defend many of its features. I also make a very big effort to respect other people's views, preferences, likes and even dislikes. I also respect Cook, even though I wouldn't like to see the next iteration move back to such a rules heavy version as 3.5 (and I'm fairly certain it won't. Fingers crossed.) And I was happy that he had joined the D&D team again, even though that meant the end of production of my preferred edition, mainly because it also meant they wanted to make a serious effort to reunite the player base, a goal I'm happy to play a part in if I can. So let's try not to lump us all together as a bunch of rude, insensitive sods crowing like whiny kids because someone told us they are taking away our toys. Criticise the individual for their individual comments. No one else on this board represents me or my views, no mater what version of the game they play. [/sblock]
As for my own speculation as to what happened: What ever it was had to be a big deal for Cook. You don't just up and leave in the middle of a major project for a minor annoyance. What that reason is ... not a clue. Prefer not to speculate. WotC, however, in my opinion, would do better just being up front about it, if for nothing more, to take the venom out of wild speculation. Because people will/are going to/are already doing it, and not in a nice way.
How this affects my view of 5e: To be honest, at game level, it doesn't. I remain curious but not enthusiastic. I remain hopeful, but I'm not getting my hopes up. I was excited to read yesterday about background and theme synergy with class for character creation and removing class and skill association. Actually, it was the first time I felt a surge of 'Ooooh, that's cool and exciting!' So, that is where I will remain. Waiting with an open mind as before, but far from sold on anything yet.
And now we know the wait til the playtest will only be a short one. Good news? I hope they aren't rushing to that date as a pure measure of damage control. I could understand if they were, but on the other hand... maybe not such a good idea. They are going to want to release something pretty decent ... otherwise it will be something akin to feeding time with the sharks.
