1) The overall feel of the game is far more high fantasy. Characters get more spells each level, receive more comic-book style supernatural powers, and the new races introduced are also relatively outlandish. The one that particularly stands out is a draconian style spin-off, now presented as one of the core races, which can breath fire at 1st level.
2) There’s been a continuation of the same sort of power creep we’ve seen over past editions. Characters of the same level can take and deal more damage than they could back in 3.5. None of the races listed in the PHB or DMG have any disadvantages listed, and they all enjoy a bonus of +2 to two attributes, along with one or more unique racial advantages.
3) The game mechanics are far more unified. Attack rolls, saves, and proficiency checks all work on the same mechanic.
4) Healing Surges. As Brianna mentioned, these seem a bit lame. The basic idea seems to be that a character can suffer a sword wound, stop for an action to take a breather, and then keep going as though nothing had happened. Predictably enough, most monsters don’t get to enjoy this advantage, which seems pretty much a one-sided bonus for player characters to use against their enemies.
5) Magic rituals are now far more firmly entrenched in the game mechanics, they even have their own chapter in the PHB. I’m not quite sure how these work in play, but it seems to fit the genre quite nicely.
6) There are now only five alignments: Lawful Good, Good, Evil, Chaotic Evil and Unaligned. Following the suggestions in the PHB this would mean that PCs only have the choice between two alignments, which seems a bit dull. Most of the gods that you’d associate with the former neutral alignments are now listed as “unaligned”.
7) Instead of Feats, characters receive special abilities every few levels in play. These are divided into three tiers, for the levels 1-10, 11-20 and 21-30 and work to funnel characters into particular career paths as they advance in level. These powers can be “at will”, “once per encounter” or “once per day”. Some of these abilities are tied to different character races.
Overall it seems like a fairly decent streamlining of the rules from 3rd edition for dungeon-crawl style games, if you like that kind of thing. There are a few tweaks here and there which made me smile (such as the kobold rogue in the MM which is able to push other kobolds into the way of incoming attacks as a special ability) but a lot of the other changes just seem seriously odd.
It’s a major overall from the 3rd edition rules, and a lot more re-balancing and streamlining has gone on. There isn’t anything much wrong with the rules as such, they’re just not tailored towards the sort of games which interest me. Here’s happy to stick with 2nd edition or the nwod for another five years, or whenever 5th edition comes out.