In some ways 4E is a step back to school principles and in others its ventured into non-D&D-like territory.
In old school D&D (OD&D,Basic, 1E) NPC's and monsters were given abilities during design as needed. There was no template, or code for assigning this stuff. 4E is back to that principle which is nice.
3E D&D was very building block oriented. Every ability, power, ect. had to be codified as a skill, feat, racial power, ect. It was very complex, allowed for a large variety of options, and very cumbersome. It was also the days where a DM feared an ability audit of his monsters from an organization more feared than the IRS-THE PLAYERS!
The tactics myth:
What 4E brings that isn't new is tactics and cooperation between players. This has always been possible although not everyone took advantage of that.
The 4E tactics thing " Now we all have powers to help and support each other" just doesn't stand up as being tactics to me.
In old school games, you could use tactics to get enemies in position, hold back some party members to flank an enemy once engaged, find defensible positions, and other such things. The type of things a pseudo medieval small unit might do if there were magic.
New school "tactics" are exercises in game logic. "Hey Bob don't move on your turn. I'm gonna smack that guy with a power that will give you +2 to hit him."
To me thats more board game mastery than tactics.
There are other differences that keep the feel of old school out of 4E.
Character growth and development:
Old school:
Characters grew as they gained levels. New abilities built on what what was learned before.
New school:
Characters are rebuilt at a new level, abilities are swapped out when they are no longer kewl enough. By the time level 30 is reached the character may no longer be able to use many powers that were used throughout his career.
Reckoning of distance and time:
Old school: feet,yards, miles, hours, days.
New school: squares, per encounter, milestones.
These are things that keep the feel from being close at all.