First off I will say that I have played DnD 3.5 for a total of 3 years, 3.75 for about 2 years, and 4th for about 1 year. I would not say that I am an expert in DnD but I feel like I have my feet wet fairly well now. I am the DM for my group and I do have a better time playing as the DM. I think I just like making characters and generating backstories a lot more than I like actually playing. So while using all 3 game systems, I never had any huge complains about that. Each has a good system to define your character in terms of gameplay and it is up to the player to make up the flare or backstory.
I will start with the positives of 4th since we actually did have a lot of fun with it. The gameplay is straight forward and my group really enjoyed that you could print out action cards. Some of the newer gamers in the groups still prefer that method and I have implemented it in my other games since then. The playing cards or action cards are a great way for the players to feel like they have everything their character can do, right in front of them. It also gives the DM an almost unlimited flexibility with the monsters since all the attacks need is an amount of damage and an effect type. It becomes really straight forward to change an attack or make it more powerful.
And really, as a DM, the best part of 4th was the math behind monster and player creation. Since Wizards disclosed all the math to generate the monsters, I was able to write excel spreadsheets to generate as many as I wanted. I had a nice little chart made where I could define a creature by type(defender, striker, etc), level, and best ability(mind, str, dex). Then it would generate the AC, Fort, Will, Ref, Attack Roll vs AC, Attack Roll vs Save(fort, will, ref), and damage(for at-will, group damage, limited use, huge attack). I was then able to use the information from the party to generate hit percentage, XP, and difficulty for the party. I used this same spreadsheet to track init and I gave the party a view of how well the fight was going. I did that by showing them a pie chart of how much health was in the encounter vs how much damage they had done.
Hope all that math didn’t confuse everyone. I think I had too much time on my hands really. But once I had that all finished, I could pump out any encounter in under 5 mins. The equations even supported creating solo monsters or large boss fights. Generally the encounters were always super balanced and the party really enjoyed the variety that I was able to throw at them. And since I wasn’t using the core monsters I was able to pull from ANY source to create the encounters. Our campaign was a little off the wall because many encounters were dreams or portals from the normal story. I used that as a game mechanic for every player to generate a story for their character’s worst nightmare. This meant that we fought everything from pokemon to the seven dwarfs, to the vampires from Twilight.
Well now I have to talk about the bad stuff. This is hard for me because I don’t like dissing a system that we had so much fun with. But if it was so much fun then why aren’t we still playing it today? I believe the core problem isn’t the online character creation that made everyone so upset. It wasn’t the limited design of the characters either. I believe it comes down to a flaw in the power design. As a DM, the way I see it is every attack has an attack roll, damage, and optional effect. That is something that is unique to 4th and I believe that is where it broke. Since every single attack(minus magic missile) has an attack roll, then it makes everyone feel like their characters are the same. Someone can’t build an awesome healer such as without first building someone who is good at attacking.
Since every spell or ability has to “Attack” a target before they cause an affect, it means that everyone is a fighter. They just happen to cause an effect with each blow. Sort of like a magic sword or something. And what that does to gameplay is that there is no real reason to pick one class over the other. They all attack and they all cause effects. The only difference is that some classes have a sub-set of effects that only they have access too. But all that means is that everyone tries to pick abilities that give them a variety of effects. Normally it is kinda fun to be a fire mage because you have so many flame spells at your command. But in 4th, that just means you have a 3d6, 2d8, and a 3d10 damage + fire damage.
I think it takes away of uniqueness of being a wizard, druid, or warlock. Everything is basically a fighter or archer with magical arrows. In earlier versions a wizard(by the end of the game), could literally know 100s of spells. There were so many ways to solve anything the DM could throw at the party. When I run 3.5 or 3.75 games, I have a lot more environmental or large-scale problems. I know I can do this because I know the game system will handle it. In 4th, it feels like your powers are only really good for attacks and it is hard to roleplay them as anything else. Now many some groups can overcome this and learn to be more flexible but with my groups, the games develop more naturally in the other game systems. With 4th edition, if it wasn’t on the game board(with miniatures), then it felt clunky and awkward.
Well that about does it for this post. I am thinking that I will write another one to talk about what I like about 3.75 so maybe some of my points will make sense. There is so much involved with playing DnD and there are so many possibilities that I am sure there are people out there who just love 4th and could never image playing anything else. To those people, I would recommend not changing. If it is not broke then don’t fix it. But if you still haven’t made the change to 4th edition then the same thing applied to you. 
I recommend holding out until 5th and everyone should keep their fingers crossed that it isn’t online only or something crazy like that.