As many who know me know - I love most anything related to gaming. I Love Pendragon (but can't find players), Traveller (which I "play by mail" on Obsidian Portal), and Dungeons and Dragons 4e (which I both play and run a campaign in).
One thing I don't much care for is the notion of having to create separate "camps" of people who feel that in order to like one game, or version, that they must somehow vilify the other version. I like what I like and I have my reasons, I am sure others feel the same about different things for their own reasons. Frankly, I would rather play Pathfinder than have no game, but given a choice, I play 4e.
That said, there were things about 3.5 that I miss. Somehow the character generation and advancement system were seemingly more organic. By this, I mean that one could internalize the process, and create new characters by combining bits of this and that, and get (usually) something that would feel right. However, this flexibility came at a price. If one cared about the power of the character (typically as measured in a combat situation), one would either choose a pure spell-caster, or mix a bunch of martial themes. Spell-casters were always diluted by multi-classing, whereas single-class martial characters could always be out-powered by the judicious admixture of multiple martial classes.
One other thing I miss by proxy, was the possibility of outright simplicity. In 3.x, a player who loved the story, but did not give a wit for tactics could play a fighter, and be quite content to close with every foe, and standing toe-to-toe, beat it until it was dead. In 4e, one has a role in a parger party. To succeed against the "recommended" challenge levels, one has to fulfill ones proscribed role within the party, as well as play well tactically. This may involve judicious movement during combat, and careful timing of when to use ones various powers. This means that some of my friends - who do not revel in strategy or tactics, and perhaps prefer the role play to the wargame aspect of D&D are left somewhat cold by this, indeed they might find that their skills are called into question by their adventurer colleagues for such crimes as being the defender and neglecting to mark their foe, or for winning initiative and leaping into combat before the wizard gets off his area effect into the assembled hoard.
One of the things that bothers me with 4e is that the promise of faster game play is only true by a modest margin. There are too many conditions to track. Even an excellent DM can miss some things, and having ones attention divided between tracking all the conditions and statuses can blind one to tactical opportunities - such as remembering to use some "setup" power at the right time. The conditions issue gets even worse when one considers how monsters are being built as the game ages. It is very, very tiring to fight a bunch of creatures that combine being insubstantial (take half damage), with a controller that weakens (the victim does half damage). Even more irritating from a player perspective is action denial, for example playing against monsters that stun, daze or dominate. When the game has become so tactical, having ones options in a turn denied to one is extremely frustrating. Of course every combat should have some pain, some risk. However, playing in a game where it seems that everyone will most likely survive, but only at the price of rounds upon rounds of heavy slogging, where a significant part of ones time is spent missing turns waiting to make a save against some effect is really not so much fun.
On the other hand, some 3e classes, such as the rogue were dreadfully nerfed. Somehow, everything he did could be done better by a Wizard (from about 7th level onward). Additionally, everything he did became a lot less likely to succeed at about the same time (foes become undead or constructs, monsters have tremor-sense or undefined anatomy). I could never enjoy a straight-up rogue in 3e.
The existing 4e hybrid system to me is a bit of a mess. Some of my friends love it mostly because they can find munchkin corner-cases of awesome power, but for the most part, I find it produces under-powered characters, even when building what was a "traditional" multi-class theme.
I hope that the new edition (and I don't know whether I will play it, but I suspect I will buy at least the rule books) will be able to weave the strands back together. That there will be some classes that are as simple to play as the 3.5 fighter, yet will be reasonably balanced with arcane characters. That typical martial characters will have far _fewer_ condition-causing powers for everyone to track. I think it is just fine that controllers can cause many different conditions. it has always been so. Less so for fighters and rangers.
I hope that common (frequently encountered) monsters (especially the weaker ones) will cause conditions far less often. That there is a recommendation to DMs to use condition-causing creatures judiciously so as not to "bore" players with them. It used to be a thing of terror and fascination that the medusa, or the gorgon had these awesome abilities. I don't want every Tom, Dick or Kobold to slow down the game with their multiple synergistic conditions combos.
I also hope that - as a result of simplification of (most of) the martial classes, that multiclassing will become easier and more organic.