The TF2 Beta now has doubled health for every class, along with (effectively) extra health for Engineer buildings and Spy Sappers.
The primary effect of this change is longer fight duration. Basically any two classes can stand out in the open shooting at each other freely without either being in too much danger. Since fights last longer, you can afford to make more stupid mistakes. If you get into a fight you can't win, you can always just run away; even a Spy can take three mid-range rockets and survive.
Speaking of Spies, this mode makes them vastly more powerful. Only the Spy has the ability to instantly kill any class and instantly nullify any building. With double health, a Spy can loiter under enemy fire until he sees a backstab opportunity. In fact, a Spy can run up to a level two Sentry while it shoots him in the face, Sap it, and walk away with a decent amount of health remaining.
Spy is King of Team!