So folks have mentioned that 5e will need to be spectacular to draw gamers away from their currently preferred editions, but it does have one thing going for it that I think hasn't been emphasized much...it'll be
new. As someone who has played a lot of systems over the years, this is not insignficant to me.
A new D&D that does a lot of what I want would interest me, even if it weren't the
perfect system. And if I'm honest with myself, my preferred system was never perfect either.
A lot of what I was hearing about 5e before Monte left intrigued me. A part of what I love about my preferred D&D has always been the complexity. I enjoy delving into the mechanics of a system and building my character over levels. So the re-inclusion of Vancian magic appeals to me.
On the flipside there is a member of my gaming group who is...not playing with a full deck, let's say.

The idea that he could take a more straightforward version of a class instead and be good to go appeals to me greatly.
I have never been a fan of all classes playing the same, and all powers built the same. But at the same time the inclusion of some at-will abilities seems like a net positive. I can't recall ever being overjoyed about the wizard using a crossbow for the first three levels of his career. Usually he just sucked it up and bought a wand. Why not just let him shoot magic missiles?
The re-emphasis on ability scores intrigues me. I'd done a lot of that ad hoc in my own games for a while, but I like the way it's more central to the design, and I like the way there are now bonuses to skills without actually having to micromanage skills.
I am interested in the idea of Backgrounds and Themes, which both feel very 2e to me. But they add a neat twist to customization that I think adds to the game. I have occasionally given my PCs a free "bonus level" in an NPC class to denote their backgrounds, and Backgrounds and Themes seem like a more elegant way of doing the same, with a bit of 2e kits thrown in.
So looking at what I know of 5e so far, it definitely feels like there are elements of several editions they're drawing on. I don't love all of them, but many of them have me intrigued, including those from editions other than my favorite.
How much of that was due to Monte's influence? I imagine a lot, though certainly not all. I have a feeling that he may have championed the return of Vancian Magic to be sure, but all the rest of it? Who knows.
I am sad to see Monte leave. I respect him as a designer even though I've never bought his stuff (I've never been much of a 3rd party product purchaser,) outside of D&D. He was why I read through all the 5e documentation to begin with.
But if the remaining designers don't simply wash out the intriguing ideas I've already read, 5e could still capture me.
At the end of the day I anticipate it will have elements of all the previous editions of D&D. I hope it will be--and to capture me as a customer it will need to be--innovative and create it's own identity that is more than merely a collection of bits and pieces that came before.
Good luck Monte Cook! Good luck D&D!