Whoever said running 4E is easier than 3.5 wasn't speaking from experience. I know 3.5 well and there was nowhere near as much bookkeeping as their is for a 4E game on a combat to combat basis. This makes combat take quite a while as the player's level and gain more encounter powers.
NP - I'll speak from experience
I had to rerun a whole combat because I screwed up on a powerful monster effect when a creature was bloodied that might have killed a party member if I hadn't forgot about it. Alot of little things to keep track of and remember running 4E. It slows the game as much as 3.5 supposedly slowed the game with too many rules.
This is no different from 3e except that you don't have to keep track of a list of 50 spells and 15 spell-like abilities of four different creatures. I don't see how "forgetting to do something" is a 4e problem and not just a problem. As DMs we forget things. Monsters in 4e only have 3 or 4 powers to keep track of
at most as opposed to at least. Personally, rerunning a combat because you
might have killed someone is a bad idea. You made the mistake, live and learn. And what ever you do - do not tell the PCs. I don't tell the PCs I forgot to do something unless it was give them treasure, then I make up for it. The reason is I don't want the players to second guess what happened. Keep a little mystery in the game. The DM doesn't reveal all of his cards. Next time they face a similar challenge you can get your chance to use that power. It makes combat different for you and them. The PCs have to react to a "new" power (I use that term loosely, ehem) and you get to redeem yourself
This is why I enjoy running thematic adventures more in 4e than in 3e. As a DM you must to learn to run your monsters like a team. It takes some practice. The players get practice as a team every session. Admittedly, they're often better at being a team then DMs. The easiest way to practice is to build an adventure around a group of monsters you're interested in. Use the same group with minor variations and you'll get better. Also, the encounters will be more challenging, more interesting (you can focus less on the rigors of tactics and more on elaborate details) but also quicker because you're taking less time.
It seems to me there are just as many rules in 4E as 3.5. And way more combat to combat bookkeeping.
The only reason why there was less book keeping is because there were so many save or die powers. However, monsters in 3e had effects that would last for 3 or 4 rounds. They had a cool down that would vary depending on the initial die roll. Because you roll the die once it's much easier to forget exactly what round you rolled it on. Was that on round one or two? The 4e effects are much easier as well. There is no "stacking" of Prone/Flanked/Stunned/Higher Ground. You just have Combat Advantage.
And sometimes it doesn't help that minis are being used for battle. Minis have no numbers, so myself and the other DM sometimes make mistakes on who has been damaged and who hasn't in large combats because we don't recall what number a particular mini is.
Love to hear some suggestions from other DMs on how they keep track of damage to a particular creature when they are using a mini with no number designation in a large scale combat. I know I get lost sometimes. It hasn't had a huge effect on the game, but it is a bit frustrating to have to keep careful track of all the movement when the minis look the same for multiple creatures. When I used numbers on a grid map, keeping track was much, much easier.
I've been using minis since 1e so it's really not a big deal. However, something I just recently picked up is a magnetic dry erase board. It's not very big, the same size as a piece of paper. It tracks initiative, hitpoints, turns, rounds, ready, and delay. I picked it up for $15 at the LGS. It does make the game a bit easier. I break the NPCs up by initiative as NPC1, NPC2, etc. Elites and Solos are NPC1 and minions are always a the last one used. I roll initiative different for the different types. It makes for a more dynamic combat as the monsters don't all go at once.
For tracking the monsters that are the "same" I'm usually only dealing with two or three. Just write a number on the base of the miniature and keep that number on your record sheet. For example, D&D minis package usually comes with several duplicates or commons. I'll number all of the same spear kobolds 1,2,3, etc. Then the next group that has a silly hat 1,2,3, etc. Granted, I don't have lots of D&D minis so I'm always borrowing. When I'll tape a piece of paper on their base with a number. I don't want to write on someone else's mini
Overall, I'm going to keep playing because my other players seem happy. But some of the luster of 4E has worn off for me. It is just another game system with different mechanics. Some I like, some I don't. I do know it isn't any easier to run than previous editions. There is a tremendous amount of bookkeeping for 4E. Even though it is resolved quickly, you have to be on top of every little change to make sure you aren't short changing anyone. That can bog down play quite a bit the more complex a particular group of monsters are. I never had this kind of problem in 3.5 when a spell either worked or it didn't, resolved in 1 round. An attack hit and did damage, end of story. So suffice it to say I'm not seeing the easier to play factor of 4E.
I'm seeing the easier to start playing. But not shorter, less complex combats. I'm seeing the opposiite as my player's level. Harder to track, longer, more complex combats that require careful awareness of how each mini moves and what effects are in place on each person on the map.
I'm beginning to long for simpler days.
Actually I think what has happened is the players are comfortable in their shoes and you're not. At third level they have about 7-8 powers. As a DM you have twice that per encounter and it varies with each encounter. That means you'll potentially have 90 different powers to manage over the course of a single game night. Overwhelming when you think of it like that
This is what I meant when I said, "build thematic encounters." By using a campaign that revolves around Goblins for the next 3 levels it allows you to get comfortable with the Goblin monsters and powers. Also, you get better at varying your encounters - mixing them up. Gradually you add new monsters to supplement the Goblins. Eventually the Orcs that supplemented Goblins become the new monsters in the campaign. It keeps you from being overwhelmed and keeps the combats interesting.
Knowing this, the prep time should include a quick tactical test of the powers within the encounter. With 3e you are familiar with the ubiquitous Power Attack/Full Attack. Well, that's gone. Now monsters vary, even when they're the "same monster". Goblins are vastly different from Hobgoblins in ways 3e couldn't. Hobgoblins are vastly different from Orcs. But Hobgoblins are also different from
Hobgoblins. This is new. And it's much more than size, stats, weapon type and damage. They have abilities and powers that suggest a style of play. When you design an encounter, work out a basic strategy with the monsters. Imagine what the monsters will be doing based on their roles. Often I'll find that there's another monster I'd like to use and it's a better fit. Try to get comfortable with the monsters
before you play the game, not during.
Hope that helps.