I think experiences with 4e are fairly varies (and that's not very surprising, given how many people play any given edition of D&D). I think GM judgement remains pretty crucial - in combat, it is especially prominent in the setting up of encounters and making choices for NPCs/monsters; out-of-comat it is crucial not just to framing skill challenges but to adjudicating the consequences of each skill check so as to reframe the unfolding situation as the challenge progresses towards its resolution. That is a different sort of GM role from (say in classic D&D) deciding the percentage chance of discovering a particular secret door, but nevertheless makes GM decision-making pretty central.
It's not just that. In our 2e game, we could expect nearly random rulings from the DM. Want to grapple a troll? Likely our 6 different DMs would give 6 different answers on exactly how that would work. One would rule it out immediately saying the troll was way to big to grapple, one would allow you to try it and then give the troll a free attack on you and make you make a dex check or fall off and take a bunch of damage, another one would come up with some convoluted rule that required 10 different checks for "realism".
If you tried to jump over something the distance you could jump would vary immensely from DM to DM. If you tried to talk to an NPC, one DM would use a charisma check and another would just rule that the NPC didn't like your face and ignore everything you said.
Meanwhile in 4e, you know what options you have. They are all listed as at-will, encounters, and daily powers. Even your Basic Attack has a stat block in Essentials and onwards to make sure everyone knows how it functions. They are written in a very specific formula with carefully laid out rules that explain how to adjudicate them. Anything you'd like to do that isn't listed in one of your powers is likely a crap shoot. After all, if your DM understand the reasons WHY there are power stat blocks and understands the balance of 4e, then allowing any actions that duplicate any power in any book is like giving someone a free feat(or couple of feats). The book discouraged stepping outside of the box because it explained the box was there for a reason.
True, the DM has the ability to frame a skill challenge. However, the book told you what the "correct" DC was for the skills at each level and how much XP to hand out based on the DCs you set. It gave you a list of skills and encouraged you to only use skills from that list. It explicitly said which stats affect which skills.
Players can read all that information and be fairly certain their DM isn't going to say "Give me a Strength based Diplomacy check, DC 47" because Diplomacy is stated in the book as being Charisma based and the DC by level has a chart. In this way, the rules remove a large amount of the decision making from the DM.
Instead, the DM uses the rules as a tool. You say "You are talking to someone, there's a skill for that...Diplomacy. It's hard, so a hard DC for your level is 26. Make a skill check and get 26 or more and your succeed."
In combat, you look at a monster's powers(of which they likely have 2 or 3) and you pick one and follow the instructions. You are making decisions, but from a lot smaller pool of options.
I'm not saying this is good or bad. But 4e does take a lot of power out from DM decisions and put them into the rules. Which is why a lot of players feel the shift into D&D Next is putting too much power back into the DMs hands. Like being able to arbitrarily decide what counts as good roleplaying and give out benefits because of it.