When 4E came out I had total nerdgasms over all the funky powers, the interactions of abilities and the wonderful crunchyness of it all. I thought it was a really revolutionary step for D&D, kind of the culmination of a direction D&D had been heading for a while. I read the books pretty obsessively, gleaning every nuance from the powers, working out optimal builds, designing adventures, and getting right into the game, all before actually playing it. It was a time when my opportunities for gaming were pretty limited, so I had a bunch of anticipation before I could actually play the game.
When I played it, I had a pretty good time. The combats were, as advertised, interesting tactical excercises, with nice emergent properties as players discovered interactions between powers and began utilising them in combat. In fact, the most fun we had with the game was just fighting a series of random combats in a dungeon. Nothing but a series of fights. So I enjoyed the game, but as time went on, I began to find it a little unsatisfying. I couldn't put my finger on it, but it just felt like the game was not for me. There was something about the combats that just felt a little empty to me. The whole game had a slightly removed-from-reality feel, that I couldn't quite place. It felt like an abstraction of a roleplaying game.
I think Vincent's essay on fictional causes has finally given me the language to describe what I think the problem was. To my mind, the most accessible of Vincent's essays on this is this one, but to go to the root of the discussion, you could start here. I'm not going to bother to restate what was said there.
Someone started a pretty abortive thread at Story Games about this, but the thread got swamped by bickering as if it was on the internet or something, so I wanted to try again here. 4E doesn't have enough fictional causes during combat, which means that the details of the fiction ceases to matter in play, especially in combat, and gets less and less important. People still care that you're saving the villagers or stealing some loot or whatever, but the small details fade into the background. Then people end up playing it like a tactical board game. Which is fine, but not what I want in a roleplaying game, y'know?
In 4E, when you want to know what's going on in a fight, what all the relevant factors are in your decision making, and what rules are going to apply to your actions in your turn, you look at the board. Every relevant fact about the situation is conveyed in information in the "real world" of play. The position of enemies is indicated by tokens or miniatures on a grid. The conditions affecting them have concrete rules that you can look at in a book. "Prone" means -2 to AC and attacks, or whatever, not "lying on the ground, with whatever effects make sense based on that".
When I play Labyrinth Lord (which I'm doing a bit at the moment), the details of the fiction are intensely important. That's because when you want to make a decision about what your character is going to do, you have to look at the fiction. Do you get an advantage when a monster is knocked down? What kind of monster is it? What knocked it down? What did it fall onto? How are you attacking it? The DM makes a judgement call, based on the details of the fiction.
In D&D, the details don't matter. You don't need to refer to the fiction at all. Everything you need to know is in the "real world". You can refer to the fiction if you want to, and you can add as much fictional content to your action as you like. The game doesn't stop you from adding to the fiction as you play. But the fiction never gives anything back.
"Page 42" is the argument I hear most often against the "4E as board game" approach. Page 42 of the DMG has rules for "Actions the Rules Don't Cover", that give guidelines for adjudicating actions that draw on the fiction to have concrete, real world affecting effects (like hit point damage). In essence, it's true that Page 42 is all about fictional causes. My sense though, is that in play the rule doesn't often play out like that. I think that elements of the fiction that are able to inflict real-world effects quickly become "game tokens", represented in the real world, with their effects on the game carefully adjudicated and deliniated. The example in the text of the DMG, and the examples I hear about in discussion are very much pre-determined, well defined game effects introduced by the GM, with an expected and defined method of interaction from the players based on the rules in the book. The opposite of fictional causes.
I'm not saying that 4E is bad game. My Life With Master, for example, is in my opinion pretty similar in this regard, and I had a good time playing that. I'm just saying that I'd rather play HeroQuest