Tony Hawk's Pro Skater HD will add three levels from Tony Hawk's Pro Skater 3 as premium DLC: Los Angeles, Airport and Canada. Along with these levels, the revert ability from THPS 3 will be included in the 400 MS Point ($4.99) DLC package.
However, the revert was previously localized to those three DLC levels only, and now Activision says all Tony Hawk HD players will receive a free update adding revert to the original levels. So if you want the three additional levels, you can snag them on December 4 for half a sawbuck or you can take the free update and up your high scores on the original lineup pulled from the first two Tony Hawk games. Or you can do both. Really it's entirely up to you.