I have a 2012 Standard DC in one of our offices and a 2012 Standard fileserver at home. Day to day, its honestly not much different than 2008 R2, but it really depends on your usage. Just like Win8, there's a lot of under the hood security and OS features, and there's a lot of upgrades to some of the more high-end server functionality.
Classic Start still works on it too, which is great because they still shoehorned a lot of that metro crap into it. All in all I like it. I wouldn't run out to upgrade all my servers to 2012 just because, but I dont see a reason to hold onto 2008 R2 as you refresh unless your business is big enough where upgrading all your CALs is going to be cost prohibitive. Just remember that the license doesnt come with the 5 baked-in user CALs like previous versions did :/
I also like the new Server Manager waaaay better than the old ones.