I guess everyone has their own preferences about what 5E should have. That's why the news of having a core system and optional rules, both for DM's and players, sounds like a good idea. This makes it even more important to have a very functional base system. D20, hitpoints, target numbers etc. will most likely stay pretty much as they were. Personally, I'm not so fond of hitpoints anymore, but I guess they are D&D.
Issue: Hit points
Something has to be done to hitpoints. Having kept track of slowly draining hitpoints of many 1000+hp monsters, I really want something else. If there will be hitpoints, then let there be some other way to give power to creatures and characters than just giving them a gazillion hitpoints - I don't want to play Dungeons and Accountants.
Minions was an attempt to reduce bookkeeping. While I like them, they are too weak. In my last session I had a powerful wizard and a large swarm of really mean bugbear minions attack the players. The PC wizard killed 90% of the minions, other pc's quickly finishing the rest, and the enemy wizard continued his flight past the PC's without a thought of staying to fight. It's good that the wizard gets his moment of shine, but that's a bit TOO much - if she would have killed a bit more than 1/2 of the minions I wouldn't have had an issue with it. Brutes have low defenses so they went down quickly. Another option is needed - looking at Savage Worlds extras is a great way of implementing minions.
There's also a semi-functional example of how to change effects of damage (which are currently none before dropping, which is boring), and the example is really close: Star Wars saga's condition track. While it might not work well just like that, it might be modified to dazed-stunned-unconscious -track. Or then characters could just have special critical -like effects instead of bonus damage, 'natural roll 18-20 dazes the target' etc - which could also interact with such a track.
This is something we might never get rid of in D&D. Maybe it's effects should be reduced though. Levels and careful balance are something that makes it sometimes very difficult and slow to create npc's and monsters. This is another thing I really like in Savage Worlds - if necessary, I can throw a completely new creature with very little thinking, something that doesn't work in games like D&D.
Addition: Latest news from DnD next hint that this issue is being addressed to. Levels are there, but with less dramatic effect!
Issue: Looks and style
While 4E design and graphics were ok, they weren't great. (See, I'm already talking as if 4E was dead. My current 4E campaign is going to end soon and I don't think I'll touch 4E again as a GM after that, if at all).
Maybe time makes memories golden, but I now miss a lot of things from 3E, even if I first didn't. And one of the things is how the core books looked and felt. I really liked the drawings, backgrounds, characters, everything. It was a Hit, something that outshines 4E big time. I REALLY hope Next grahpic design will be closer to 3E than 4E!
Issue: XP and killing
Of course players want to loot every corner of a dungeon and kill everything they meet - they'll get xp for killing. The team works like an oiled machine grinding every drip of xp available. While some may enjoy it, I usually think it's away from the story. I agree that xp for killing monsters is essential part of D&D, there should be some way to get rid of unnecessary fights.
Oh dear. Paladins. Brave warriors that have strong might and are champions of their gods. Or Laser disco spheres? I say they should be divinely enhanced martial characters - I really hate how paladins were implemented in 4E. I even played a low level evil one for a while, and I was able to make quite martial type out of it (a minotaur in an evil campaign) and enjoyed playing it - but the second route a paladin can take is something I'd rather not see again; many players try to make most effective characters, which is likely to result in laser disco spheres showing up in games.
Issue: Magic items
I might have attempted to convert my 4E campaign to Savage Worlds, if it wasn't for the magic items. Players wouldn't want to lose the items, and I hate items being that important, especially as there is still so many magic items.
Players have planned their characters far beyond their current level, know exactly what weapons and other items they want and when I think I've fond a cool magic item I want to give them after browsing the books, they sigh and put it into sack to be sold or demolished into residuum. And suggested shopping lists are the most horrible idea ever, I've mentioned before that it makes the game feel like players are children sitting around christmas tree.
Issue: Electronic subscription almost must
I want to play a tabletop game, not to spend another n+1 hours on my computer, trying to use programs that are too heavy for my mini-laptop in order to create some monsters for my game or to get up-to-date powers for my character.
Part of this issue is amount of errata made to the core books. This feels to make the core books almost worthless - well, not completely, but there's so much errata that I've began to doubt pretty much everything in the core books. I really like to have solid rpg books in my hands, and the situation with 4E started to moved into 'you don't need core books, you need a computer in your gaming table'.
Issue: Core book contents
I used to play and run games with 3(.5)E using just the three core books - these books had it all! I was quite unhappy with what the three 4E core books gave, from the beginning it looked like there should be more. Well, I guess it was just very commercial product.
Currently, I'm really hooked to Savage Worlds; if DnD next doesn't give me enough materials in the three core books (assuming the format will be same), I'm going to pass the game. I've always (well, since 3E) liked D&D and if I like the game and I get all the basic stuff in the core books I'll buy those three core books, but if I'm required to buy more in order to have enjoyable games with some variety, and I have an alternative of continuing great games with my €10 Savage Worlds rulebook that gives me pretty much it all, why would I even think of getting the new expensive books that give less than this €10 book?
Rumors sound promising
enWorld 5e page has a lot of information about DnD next - WotC doesn't want to call it 5th edition, even if many of us use that term. Many things I've read from there are promising, and seem to be addressing to some of my worries.
Hit points and levels are going to be less of an issue now, it seems. Focus will be on tabletop again. I'll have to say I'm really curious about the new edition, but I'm reserved - after 4E I think I have reason to (and remember, I liked 4E initially).
I'm eagerly waiting to hear more about the game and to attend the open playtesting!