My group and I have found 4e us a really strong 1e vibe, but its rather hard to explain why. Here is what occurs to me:
* 4e is definitely easier to run and prep for, and DM fiat and off-the-cuff decisions are encouraged- that is a lot like 1e AD&D to me.
* The PoL default setting and the tone of monsters in the game seem very "old school" to me and my group. Things are kept more vague from the player's point of view, and the world is a big, dark, scary place.
* 4e's ease of rules use and rules-transparency is much like 1e. I've not played a D&D game in 3e where we didn't need to refer to the books 10+ times per session. With 4e, we might refer to the books once every 2 or 3 sessions. The game flows much better and keeps moving, which I have found draws the players in more.
* Kinda related to the previous point, but worrying less about rules means IME that the players get more absorbed in the story and world. Again, this reminds me a lot of our 1e days.
* 4e is less focused on rules mastery, and more focused on teamwork and tactics. 3e was strongly in the rules mastery camp, and if you wanted to, you could build a PC with no weaknesses. Thats fine for some players, but it did tend to lead to "lone wolf" kinds of situations in play, where PCs did their own thing on adventures, and didn't work or play well together. 4e has a stronger focus on class roles, with each PC really good at a few things, OK at a broader range of things, but is weak in one or two areas. PCs need each other to survive in 4e, and splitting the party is a sure way to die- that is a VERY strong 1e vibe.
* Now I know some folks will strongly disagree here, but I have found 4e PCs to be MUCH less powerful than 3e or 2e PCs in their equivalent systems. True, 4e PCs start with more HP and are more competent in relation to previous editions, but in comparison to monster and other NPCs in the world, the PCs are MUCH less powerful than in previous editions. I'm seeing my players taking a much more cautious approach to adventuring, because the next thing you encounter, even if its of equal power to you, could finish you off. That simply wasn't true at all in previous versions of the game.
* Maybe this is just my group, but I'm seeing the formation and execution or more "wahoo" plans than I did in 3e. For my group, 3e was too sterile and every rule possibility was spelled out, so people were reluctant to try something not explicitly stated. Now in 4e, my players are using their powers and rituals in more creative ways that the rules probably didn't intend, but that work anyway- and we're having a blast! My players have also gotten really crative in describing what their powers look like or how their character pulls off their action, even to the point of describing what happens on a miss! This reminds me a lot of the 1e/2e days of my group.