This is a huge and welcome change! Considering that the change before was 1/2/3% agility, the expertise ends up being way better. Sort of like how N Sync was way better than Backstreet boys. Not that I would know what they sounded like.... or care, um... yeah.
The thing is, the agility change was nice, but the Shaman community didn't think it was scaling very nicely at the moment. While Shaman gear has tons of agility, it was only adding about 20-25 agility for the enhancement shaman in the best of the best gear. While that's a pretty hefty number think about what getting all that expertise gets us and what it will allow Blizzard to do from now on.
Right now we need a 26 Expertise rating to get to our expertise cap. We've covered the importance of Expertise rating here.
Now, getting to that cap requires us to seek out some really odd pieces of gear. Even then, we'd be way far under the expertise cap. So then, we'd gem every single red slot or any other gem slot we could afford with expertise oftentimes forgoing gem socket bonuses that I love so much.
So instead of gemming every single slot with +16 Expertise gems, we get to fit those sockets with some of the more fun stuff. Like +32 Attack Power, or maybe some crit with the +16 Crit gem, or really whatever you think you're needing at the moment. But if you go for spirit gems, I'll find you, give you a wet willy, a wedgie, and noogie so hard that your hair will never grow back in that spot.
9 expertise is quite a lot. That's approximately 74 expertise rating (it depends on how much expertise you already have) which opens up more than four gem slots for other stuff. I would sure love to have 132 extra attack power from four extra gem slots. It sounds so delicious, I just drooled on my keyboard and think I need to wipe myself up. brb.
Ok, back. The other thing this addresses is itemization in Ulduar. While we share mail gear pieces with Hunters, there are very few pieces of mail gear with expertise because while we Enhancement shamans crave expertise, hunter can't do anything with them unless they want to melee which is really cute and silly and should be attempted pronto right after writing this post. So since they want us to continue fighting for gear, they want to help us out in the Expertise department since they probably won't plan on making mail gear that is only useful to enhancement shaman and not for anyone else.
Anywho, nice change. Looking forward to actually seeing some loot from Ulduar to see how it'll pan out.