Do you have any quibbles with D&D Next's rules?
The biggest concern I have right now is with the basic math for ability checks and skills, which is extremely swingy and makes even expert characters very likely to fail at actions that you'd expect them to succeed at a large majority of the time.
For example, take a Thief with an 18 (+4) Dexterity and 1d6 skill die, and he will fail trying to pick a simple lock (DC 15) about 1/3 of the time. This is one of the most dexterous people possible, trained in the task, and he still fails at picking the easiest lock in the game that often? He'll fail more often than not when trying to pick a typical lock (DC 20). And if he tries to pick an elaborate lock (DC 25), he'll fail about 2/3 of the time. Want to pick a magical lock? Its DC 30. So you need to roll a 20 on the D20, a 5 or 6 on your skill die, AND have an 18+ ability score. I don't even want to calculate the probability, but it's probably less than a 5% chance of success. And again, this is one of the most talented prodigies in the world who is trained at picking locks!
And this isn't the only example of ridiculously high DCs. An 18 hour forced march is a DC 25 Con check! Most people couldn't ever succeed on that check. I guess 99.9% of people would fail boot camp in DnD's world.
But what about at higher levels? Surely higher level characters are a lot better at things? Actually, not much. Bounded Accuracy and all. Skill dice only go up from d6 (avg. 3.5) to d12 (avg. 6.5). So a high level character is really only getting +3 on average more than his low level counterparts.
It gets even worse when you realize most characters won't have an 18 or 20 ability score at the task they're attempting. Most characters will only have that high of a score in one or maybe two abilities, and the rest will be no more than 14 or so, assuming you use the standard array. An average person, with a 10, gets no bonus on his roll at all. And characters only have four skills to help them, and skills are pretty specific. So the large majority of the time, characters are going to fail even "moderate" difficulty tasks that they attempt. And if these "great heroes" dare to attempt something "hard?" Have fun with that! Be prepared to fail 75-95% of the time, unless that happens to be one of your four skills, and then you'll "only" fail about 1/2 or 2/3 of the time.
The other problem is, even taking the most expert character possible, a 20 ability score with a d12 skill die, it's still possible to fail easy actions. They try to address this with a feat that makes your minimum roll 10, but feats are optional, and even if they weren't optional, feats should
never be used to fix the math of the basic game.