I haven't played in a 5e playtest yet and I haven't even read the docs all the way through, so please feel free to dismiss this post as the vague impressions of an under-informed idiot.
That being said, my beef with the most recent draft of the D&D Next playtest docs is the same one I had with 4e: my own personal D&D sweet spot, the hard-scrabble death-at-any-moment fiasco of levels 1-3, is no longer supported. Here's a simple example of why my style of play doesn't work with these rules: The pregen halfling rogue and elf mage each have 16 hit points. A standard kobold's spear does d8-2 damage, an orc's axe does d8+1. Crits do max damage, rather than extra damage.
Stop me if I'm getting any of this wrong, but it looks like that means these starting wimps can't be killed by a single blow from baseline opposition. For me, all other questions about what should and shouldn't be in the new edition pale in comparison to this simple issue. If by the numbers I can't murder your starting PC with a single lousy orc-stab, I don't want to play. It's that effing simple for me.
Depending on the edition and the hit dice used and the Con rules, some PCs have always had enough hit points to be able to shrug off that first strike. Even in OD&D a fighter can start with 7 hit points when most monsters do only d6. But most PCs in most editions are vulnerable to one or two blows from any random goon and that's the way I like it.
Back when 4e came out I agreed with the observation that 1st level 4e PCs read like 4th level or so characters under previously editions. The run of Wessex where each PC was from a different system supported that thesis. Zak's first level 4e dude outperformed other characters of second or higher level. The power level has been noticeably toned down, but I still say that an elf MU that can cast 3 first level spells per day and an unlimited number of magic missiles and shocking grasps ain't no 1st level character in my book.
But Jeff, once the modules are implemented it'll all become clear that your kind of D&D is well supported, you might be thinking. That may be so. But let me tell you the bigass problem with this modular system: it will needlessly complicate any published adventures. Will the adventures be written for all possible module combos? Will some be horribly broken with the wrong modules in play? Will a starter adventure written for Elfy McInfiniteMissiles even work as a reasonable challenge for starting characters run with the OSR-friendly modules? WotC's track record on published adventures is already dubious in my opinion, this module approach will only make them wonkier.
I like simple solutions to problems whenever possible. Here's the one I advocated back at the start of 4e: tell the 4e fans to start at a higher level. I've played many campaigns where we skipped the rat-punching, die-from-nicking-yourself-while-shaving stage. The way we did that was to build 3rd or 4th level characters. That's what the original Dark Sun rules said to do right in the book, right? Why can't we go back to that approach? Me and my fellow Old School sadomasochists get to play levels 1 to 3 (or whatever) and all the sane players just start at level 4 or so.
I've raised this idea before and at least a couple of 4e fans pushed back at it, claiming that it was unfair of me to suggest that they shouldn't get to play through all twenty levels. (The unquestioned expectation that their PC will survive that long is symptomatic of the huge gulf in playstyle that the poor bastards at WotC have to bridge.) So instead, here's a suggestion for WotC: level zero. Don't stick it in a sidebar or an appendix or otherwise marginalize it. Just write into the main body of the rules a level 0 for each class that more closely cleaves to the 3 hit point, one spell per day, crappy thief percentage losers we all know and love.