One of the core things I aim for in building an RPG is rapid combat. It should be easy for the GM to select opponents and set up a combat. It should be easy to figure out what you can do and what happens when you do a particular thing. It should also be difficult to figure out which of the things you can do is the optimal thing. The latest DnD blog post talks a bit about their ideas for making monsters and opponents and seems poised to provide an enormous list of different ways to approach it. GMs will be able to build characters from scratch, build enemy characters on monster templates, and customize their own monsters.
I remember the old days of monster creation in 3rd ed. and I do not remember those days fondly. Building a high level opponent required hours of effort to construct their feat trees, stats, and gear even if you weren't building a caster... and let us not talk about how great it was to put three hours into an NPCs spell selection to have them die on the first round without even getting to get one of those ever so carefully chosen spells off. Dragons were awful too because they always had immense spell lists that should be complete just in case but which pretty much never came up in the end because why use spells when you have a breath weapon?
Next seems to be trying to find some kind of middle ground between the laborious precision of 3rd and the lack of feel that 4th suffered from. After all, we all want the GM to be able to build monsters quickly and know how tough a given fight will be but we also don't want the treadmill feeling where no difference is apparent upon gaining levels that plagued 4th. When every gain of +1 the players achieve is instantly matched by a +1 on the part of the monsters you just don't *feel* like anything is happening. Right now there is no way to know how well they will succeed as it is just hype and hope and anyone can put together a good elevator pitch for a system. The proof is in the numbers.
However, one thing they still suffer from is a bizarre casting system. Spell slots make no sense and I can't figure out what kind of lore they are drawing from or feel they are trying to achieve. Making a spellcaster enemy is still going to require a huge spell list and tedious bookkeeping to track their slots remaining. Fundamentally I just don't understand how they arrived at this Vancian / spell point chimera. I recognize that they were trying desperately to find some sort of compromise between the new players and the grognards but I think they really should have come up with something new and better instead of just sewing on parts from discarded systems until they stopped from exhaustion and called it complete.
Magic and its mechanics are a huge part of a system's core and smashing it together like this is not the right choice. The old Vancian system is a relic, a random bit of stuff left over from a previous era. Perhaps the 4th model didn't grab people but the solution is to build something new and great not to simply serve up the same old disaster with a new and confusing twist.