People keep saying "it's just like 3e!" but I'm just not seeing it. It has the same ability score bonuses (a uniform +/1 bonus per 2 points above or below 10), you roll against a DC with the higher the result the better (as opposed to THAC0 and countless percentile tables), it has feats and ... that's about it. The skills remind me much more of 2e's nonweapon proficiencies than 3e's skills, the spells are written in prose, the themes are alot like 2e kits, etc.
The similarities to 3E are there, in my view, but it's not identical.
The similarities include:
*a standard action resolution method (roll d20, add stat mod + skill mod, beat DC);
*a regularised action economy for combat;
*turn-by-turn initiative;
*PCs build out of race, class, skills (=background) & feats (=theme);
*buff spells are important;
*much of the flavour is AD&D-ish, but it's been made more mechanically standard and rigorous.
There are differences too, obviously. Some - like the difference that flat maths should make to encounter design - aren't showing up in a low level playtest. Others, like at-will spells and "hit dice", owe something to 4e.
As a 4e GM I would say that it falls on the 3E (and AD&D) side of the great divide, because it has no mechanics that encourage any focus on the encounter as the site of play, and many mechanics (lots of daily spells, spell durations in minutes and hours, etc) that militate against this. Whereas everything in 4e pushes towards the encounter as the locus of play, with the day (and the extended rest it brings with it) as a secondary concern.
So far, I dislike the hidden math in the playtest (weapon damage dice changed by class) which is entirely, the return of x/minutes casting and combat buff spell (fully introduced in 3e and abandoned in 4e), the return of book referencing statblocks (abandoned in 4e) and the return of prose spells (abandoned in 3e).
The spell durations and buffs go to the substance of play and the differences from 4e. The style of monsters, statblocks and spells is not as deep an issue, but certainly goes to ease of use and elegance of presentation.