BUT, what I would say is that this is exactly how people played 4e IME. Games were very 'ad-hoc' in terms of where the action went and what players were going to attempt to do, and the game was VERY open ended. I think this is very similar to the experience that people like
@pemerton had (judging from his rather extensive play descriptions and postings).
In fact, in the game I ran at least, there was very little worrying about details of rules and fiddling with rule mechanics. People utilized the rules as a baseline, and fairly often a PC would simply invoke a power or something like that, but the types of situations and narrative that were evolved out of it, and how the narrative fed back into the system, were very loose and open-ended.
Part of this is because we evolved an approach to play which, IMHO, is best suited to 4e. It is a very 'gonzo' kind of 'action movie' type of play where there are constantly things happening and the scenery changes constantly. Everything is very dynamic, there is loads of plot associated with everything that is happening, etc. You NEVER just get some kind of encounter where the PCs run into 'some orcs' or something like that. There are always stakes, there's always narrative points being decided, goals to achieve, etc. So if you ran into orcs then you've got some sort of agenda, to negotiate, to make sure they don't do something, to get something from them, whatever. It is never really just a matter of "kill or be killed" except maybe in a very few cases where that becomes dramatically appropriate (IE maybe in a boss encounter or something).
Generally the action is heavily, or exclusively, driven by player choices and expressed interests. It isn't normal in this sort of play to have the GM simply interject some situation because he thinks it 'should be there' or something like that. There's logical narrative consistency, but there's also the agenda of play.
That agenda is very much "have fun". The rule of cool is pretty close to the prime directive of this kind of play. I should point out that 4e, as written, at least hints at this kind of thing. It talks about 'skipping to the action' and eschews complex rules to adjudicate things like exploration, while leaving plenty of material there so that when exploration is relevant and important and interesting that you can manage it (IE probably with an SC).