Long time d20 (and variants) player here. Not as long as some, but long enough to have played 2nd Edition when it was still current.
IMHO, 5th Edition's success will come down to their acceptance of the OGL (Open Gaming Licence), which we will discover in the coming days. All signs point to no, but Wizards might surprise us yet.
For those who don't know, the OGL was introduced in the 3rd edition (and continued its minor update, v3.5) of D&D. It was truly revolutionary. The OGL not only permitted players to redistribute the base rule system as they wished, including publishing it online for free almost in its entirety, but empowered players, writers, and campaign masters to edit, change and adapt the rules as they saw fit -- and publish those changes, as long as they too were under the OGL. It's open source for gaming systems.
One of the leading benefits of this was the publication of "Adventure Paths". As the OGL did not cover game worlds, only the mechanics and rules of the game, any writer or publishing company with a solid working knowledge of the game could create, publish, and distribute (freely or for profit) their own adventures, rules variations, optional mechanics, and thousands of various changes. One of the leading companies was Paizo, who specialized in publishing these so-called Adventure Paths. They were not the only ones. For example, I personally published a Pathfinder flavoured novel about a kobold, "Ren of Atikala", set in the original world of Drathari (oblig. plug: http://www.amazon.com/dp/B00EZ...). Using the OGL, I am able to legally use, alter, and draw inspiration from the rules and mechanics of OGL-licensed publications and create original works.
As I said earlier, it's open-source for gaming systems.
Between 3rd edition and v3.5, this was the state of D&D for almost 8 years, until June of 2008, when D&D 4th Edition was released. Unfortunately, D&D 4th Edition used a different version of the OGL, which was much more restrictive in what it permitted players, authors, and creators to edit, change, and redistribute (IIRC, it was essentially, "you may only reprint the *name* of the rule, and then reference the Player's Handbook", which meant if you were playing Star Wars you had to look up Power Attack in the D&D Player's Handbook... ugh).
Because of this change, and the simplifications made to the rules system which were often disfavourably compared to a video game, many players took a distinct, sight-unseen dislike to 4th Edition.
This restrictive change to the OGL also strongly disinsentivised Paizo from publishing Adventure Paths. After some internal discussion, it was decided that 4th Edition was not for them, and released a revised version of v3.5 of Dungeons and Dragons, known as the Pathfinder RPG (sometimes informally referred to by the player base as D&D v3.75), specifically intended to be backwards compatible with v3.5 of Dungeons and Dragons material. It was published shortly after 4th Edition's debut.
For many reasons -- a feeling that v3.5 was "good enough", Paizo's open-beta policy and staunch support of the OGL even for expansion books, and for viewing companies such as Green Ronin as allies rather than competitors -- Pathfinder has flourished in the wake of the relatively-poorly received 4th edition and is now a common staple at Roleplaying conventions and tabletop gaming communities, where previously only Dungeons and Dragons was played.
D&D Next seems, to me, to be squarely aimed directly at bringing Pathfinder converts back into the fold, promising to address some of the issues in both 4th Edition and Pathfinder, by providing a linearly scaling advancement, reducing preparation time for Game Masters, and simplifying many poorly thought out and complicated legacy rules which most players will admit probably need to go.
For me, though, D&D Next will live or die the same death 4th Edition did, based on its acceptance of OGL. Gamers typically play the most popular gaming system, even if it's not necessarily the best. If 5th Edition doesn't have a full OGL, then irrespective of what it does wrong or what it does right, Pathfinder (and the huge-mongous amount of compatible 3rd party expansions, modifications, and adventures) will just crush it.
Paizo knows this, though, and I think they're afraid. They recently announced Pathfinder Unchained, a variant (but still, in many ways, compatible and familiar) reworking of many base classes to free them of "legacy cruft". Clearly, this change is a counter-point to 5th Edition, and Paizo's platform of "small, incremental change" has worked well for them in the past... but the first OGL version of Dungeons and Dragons is now 14 years old and there is a feeling, in some corners, that a true revolution is needed.
It is clear that the future is currently in flux, and on the year of Dungeons and Dragons's 40th birthday I can't help but shake a distinct feeling that, for Wizards of the Coast, D&D Next will either be the product that restores Dungeons and Dragons to its former glory as the undisputed champion of tabletop roleplaying systems, or the anchor that drags the brand down to a final, well earned resting place in the annals of roleplaying history.
The 5th Edition organised play campaign seems interesting, though.