Well, Stealth Rock is still as prevalent as ever. Its very crucial in the demise of Dragonite and Volcarona, two large threats. Its still a staple move on all teams.
A couple of abilities got changed effects, but the only one worth noting is Storm Drain. Storm Drain now absorbs the Water-type attacks, and raises the users Sp.A by one level.
The Dream World was introduced in Pokemon Black and White, and it allowed some Pokemon to have access to three abilities, and nearly every Pokemon has an additional ability to what they had before. It gave players things like Drizzle Politoed, Drought Ninetales and Multiscale Dragonite (Multiscale is a new ability that reduces damage taken by 50% as long as the Pokemon's HP is full). Expect about 50% of your battles to feature some kind of weather, either Rain, Sand or Sun.