I've been considering D&D Next a fair amount these past weeks, and the reason why I'm so excited about it despite a lack of any sustained play experience. I think it has far more to do with the idea of a new edition than any concrete or assumed aspects of it. I was equally excited by the prospects of 3e, 3.5e and 4e, so it's not surprising at all that Next has been on my mind a lot lately.
4e was a step in a completely different direction over 3e, but the impetus behind the change has been more or less consistent for all new editions: in a word, simplicity. THAC0 is still a headache despite quite a few years of play (including pc gaming), and is basically the only reason we haven't ever gone back to try classic 2e modules (though that prospect is becoming far more realistic with Next). 3e was exciting because of the d20 system, and it seems highly unlikely that it will ever disappear from the game.
Similarly, the powers system in 4e was supposed to make for a smoother combat experience, with a character's options clearly laid out to avoid excessive rulebook scanning. Everyone in our group was initially excited by 4e, but we had no idea how it would play out over time.
Despite the initial push for simplicity, both 3e and 4e became bloated messes. I don't have high hopes for Next avoiding this trap. The push for profitability on the side of WoTC (and thus more content for sale), combined with the need for players (particularly power-gamers) to dream up better, faster and stronger builds, will mean that in about five years all interested parties will have dissected the system enough to start dreaming of something newer and more streamlined.
There isn't necessarily anything wrong with this process. For me, the game is about exploring the system as much as any particular adventure. For that reason, I will continue to be excited about the potential of Next and anything else that will come down the pipe.