Well, the thing is... the Alpha pdf files are exactly what you are talking about: the changes that differ from 3.X rules.
Basically, anything not included in the Alpha pdfs are assumed to be the same as in 3.5e.
When the Beta comes out, it will be a full book, with all rules needed to play by itself (don't need to refer to the 3.5e rules for anything).
If what you are meaning is a thumbnail description of what's been changed.. well, you'll need someone who's familiar with the Alpha pdfs to explain that. Which is what we can do for you here.
Here's the basics of what's been changed:
- Races: Changed to be more uniform in bonuses (overall +2 ability score bonus, etc), as well as a slight boost to compete with splatbook races that came out after 3.5e.
- Classes: Base classes are cleaned up, tweaked and made a bit more clear. On top of that (or possibly as a higher priority), they've been improved to be able to compete against Splatbook base classes, and to give a reason to NOT just multiclass or head into a PrC asap.
This means Wizards, Sorcerers, and Fighter especially are given new sets of class abilities.
- Spells: Fixed problem spells that caused gamestopping issues, and a philosophical change to Save or Die/Do Nothing spells (mostly changing them to more saves or straight HP damage).
- Combat: In order to fix Grappling and to make combat maneuvers like Trip, Disarm, etc, more appealing and less scary to attempt to use, they made what's called a "CMB, Combat Maneuver Bonus". Use the same stat for doing anything, making attempting or resisting these things easier to adjudicate during combat.
- Magic Items: Philosophical change in how Stat boosting items are given out. An attempt to trim the Xmas tree effect.
- Fundemental Change... No XP Costs/Penalties.
Favored Class gives a bonus, instead of altering xp penalties... since no more xp penalties for multiclassing.
Spells and more importantly, Magic Items, no longer require XP. Spells with xp costs now have a gold cost (Wish has been toned down to compensate, etc), and magic items assume the cost of the Feat covers the xp that used to be required, so getting the Feat basically means you get that set of magic items at half price (but need to spend time).
There are likely quite a few changes I've missed, but the rest are all fairly minor compared to these big ones. They are the fundemental changes being made to the game.
Keep in mind though, that some of the specifics (numbers, feat requisites, spell descriptions, etc) are likely or have been acknowledged to have been changed for the Beta.