Less rules means more freedom... but it also means more responsibility on the part of the DM to make smart, fair, and interesting decisions. And if you DON'T have a good one, the game is more likely to be less than you want it to be.
I do think there is a very big difference between how 5E works and how AD&D works. And it isn't actually on the more/less rules axis.
We've tended to think "more rules" means "fewer chances for the DM to make a bad ruling", but that's not really the case. I believe, very strongly, that what a good RPG really needs is a good baseline from which rulings can be made. It's something that AD&D doesn't have; instead you have a plethora of subsystems for dealing with different situations. What happens if someone needs to climb a cliff face? In core AD&D, only the thief could do it, unless the DM made a ruling. Then, as more books came along, they began to fill up with rulings for these sorts of situations.
But, due to the way they were constructed, they all used different systems. There wasn't a real baseline to draw from. More modern systems unified the mechanics a lot more, and so it is a lot easier to make ruling on the fly as everything sort of works the same way.
One of my big problems with 3E is how obscure the system can be. There are a lot of DCs in the rules, sure enough, but the system is so erratic about giving bonuses to characters that they're not really comparable. Synergy bonuses were responsible for the Diplomacy skill working on a completely different scale than every other skill - it was quite possible for Diplomacy to be +6 above any other skill the character had. Then, when you added in the effects of feats, magic items and other bonuses, knowing what a "typical" bonus was meant to be was tremendously hard. The less said about how Challenge Ratings were constructed, the better, especially with regard to NPCs.
4E, in my opinion, had the right idea with a unified skill system that wasn't as erratic as 3E and with sample DCs. However, the construction of how it worked (1/2 level bonus in particular) still had a number of problems that I wasn't happy with.
I'm hoping that the bounded accuracy system in 5E will work, especially as it also unifies attack bonus and saving throws into the equation.
Cheers!