Couple things I would like to see in 5e Next are:
In 4e, every battle without fail takes over an hour, usually close to 2 hours. This is with very experienced players, both in general (most have played D&D over 15 years) and with 4e (Been playing it since it came out, so 4+ years). The group is a pretty well-oiled machine and work as a team.
The sad thing is within the first 20 minutes, the battle is pretty much decided. You know the heroes will win (barring an epic critical hot streak), but it still drags on and on for an hour or two. This is the point everyone becomes bored and goes on auto pilot. You have spent your fun encounter powers, you don’t want to waste dailies because the issue is not in doubt, so you plug away for hours. You have sized up the monsters and their powers, they have nothing that the defender and heal-bot can’t easily absorb. So all that’s left is long slog. Once in a while a natural “20” will break the monotony and spark a little excitement.
The running joke we have with 4e, especially if you play with the recent offical modules, is you take 10 steps and then roll for initiative. We are playing Assault on Nightwyrm Fortress now and its extremely linear and the 10 step and roll rule is in full effect. It has been a yawnfest so far.
We have read the materials and are trying the playtest next week. We have high hopes. We enjoyed 3.5e and earlier versions many times more than we do 4e. The biggest gripes we had with 3.5e were the lack of options for fighters, a few players with the “his player is more powerful than mine” syndrome, and the complexity of things like grapple, etc.
One thing we have seen in all versions, is the core rules are usually tight and organized. So are the first 6 books or so, then the content quality drops off. It’s usually the later content that allows for the really broken crazy-powerful characters and weighs down and dilutes the rules.