The Assassin's Alchemist Stone originally came packing +54 Critical Strike Rating, but now carries +108 Attack Power instead. The caster version, the Sorcerer's Alchemist Stone, has shifted over to +63 Damage/Healing from its original +54 Spell Hit Rating.
I can't speak for everyone, but those seem to be pretty good changes to me. Of course, my main is one of the classes/specs that don't need much Spell Hit, so I'm probably rather biased in that area. If you'd like to take a look at a screenshot of the updated stats for the Alchemist Stones, just hop on past the jump.
Screenshots are courtesy of World of Raids.