Freedom, truth, love, beauty.
D&D 4th is still D&D, and It’s Great
You can still take on the role of a human, elf, dwarf, or halfling. Your character can still be a fighter, cleric, wizards, or thief (a.k.a. rogue). You are still playing as a hero in a fantasy world of magic and evil monsters. Speaking of which, all the monsters you would expect to fight are here, including goblins, orcs, giants, dragons, mind flayers, beholders, and oozes and jellies.
With 4th Edition the game fully embraces its lineage of miniatures combat simulations by making combat extremely tactical. Miniatures are strongly recommended. At the least paper chits will be necessary since so many of the available abilities move pieces around on the board. Play-by-post will be very difficult.
Magic users’ abilities have been toned down while non-magic users gain additional powers that make them more useful late in the game. This makes high-level play more interesting.
There are a couple new races and classes that are OK, but I do not find them terribly exciting, personally. The enhanced focus on use of minis is a little off-putting, especially since the D&D-brand minis are lacking in models to use as characters and monsters from the monster manual. The books are a little sterile in their design, I don’t care for the art direction, and everything is expensive (the first published adventure is $30, but I think should only be half-that).
But overall this is very good stuff. The game is easier to setup and run. It is more fun to play. And it has taken much of the best game technology developments since it’s last major edition, learned their lessons, and made a game that feels like “original Dungeons & Dragons” while being more fun, and more heroic, to play.