I use multiple RPG systems and D&D 3.0 is one of them. In its surrent version the 4th edition is definitely not for me. I read the core books, finding some changes and ideas I really liked, but as a whole the game is unplayable for me and my group.
It would be possible to modify the game so that I would like it without discarding the main ideas, but, sadly, I don't expect it to happen.
The main changes D&D 4.0 needs to win me:
1. More fluff for players. Descriptions of races speak nearly exclusively of their virtues and strongly focus on combat and adventuring aspects. They are advertisements, not something I may base my character's background on. If dragonborn value honor and valor, how does it shape their society? How are all kinds of non-combatants treated? What do they do to those who betray these values? If clans and traditions are important to dwarves, how does a clan's structure look like? Who is in charge there? How are titles and positions inherited? What are male and female responsibilities?
I understand that PCs are heroes, not common members of their races and societies. But they come from somewhere. To be able to play my character as something more than a skirmish miniature I need to know what experiences shaped him, what could he come to love or hate. I cannot roleplay in void.
2. More monster fluff for DM. I felt really insulted by MM consisting of nothing more than statblocks. Bare numbers mean nothing - a monster needs ecology. Where does it live? If it's not solitary, how big the groups are and how organized? Why is it dangerous, why does it attack people or do some other nasty things? What other monsters may it cooperate with, why and for what goals?
To be able to prepare an adventure with monsters I need to know how they interact. Without it all I may do is putting them randomly in dungeon rooms. Of course, I can make the fluff up myself - but then, why would I play a game that only gives me half the monster manual instead of a whole one (even if it had only half the monsters)?
3. Tools for creating nonlinear adventures. All the system gives me are combat encounters and skill challanges, The skill challanges have no connection with what they represent - I need to select skills and difficulties, but they are based on party level, not on what the challenge is about. As a result, I need to either predict everything what my players will do (railroading them whan they do something else) or improvise most of the interactions.
My adventures typically consist of NPCs and locations, with little fixed "plot". I don't know what the players will do. If they decide to sneak and search baron's rooms in the night instead of fighting him or negotiating, I must be able to decide how hard it will be based on how rich and how paranoid he is - and, possibly, on what the party did to him previously. Skill challanges are a great tool, but to be really useful they need rules to determine skills and difficulties based on what they are to represent.
4. Consistent world, taking into account powers that are present in it. It was bad enough with 3.0 and middleage-like castles giving no protection against low-level mage with Fly and Fireball. It is even worse in 4.0 with every eldarin able to teleport for short distances. Both are results of designing the system with only skirmish combat in mind and disregarding how the world as a whole works.
Sometimes it goes the other way, like with paladins - now of any alignment, but limited by the mechanics to powers representing light and glory. If we are to have evil paladins, put some dark, vile and thecherous powers on their list.
5. Call things what they are, instead of giving strange and confusing explanations. Hit points would work well as either lucky dodges (with no powers described as healing) or as real wounds (with heroes being just supernaturally hard) - but not as both at the same time. While HPs are the example most often used, there are other similar issues in the game. Correcting them would help putting the game world and the mechanics in line and greatly improve immersion.
