For me, I feel like he played completely against type, dad-pants and all. He was a father, a husband, a real human being that you could relate to. The same went for all the characters. I'm not sure if it's the laid back dress of Hawaiians or the fact that the makeup crew did minimal makeup for everyone, but it felt like a story that you would hear at a friend's backyard bbq (they even had one in the movie). From the cheating wife who wanted a thrill out of life and it cost her in the end, to the messed up older daughter (played absolutely brilliantly by someone who I never would have thought could pull it off) to the friends who were torn about whose side to take in everything. It was all so real.
It was also incredibly sad. No one wants to hear stories like this, about an inevitable, could-have-been-prevented tragedy. No one wants to watch a family get pulled apart at the seams. But it was just so good. I think it deserves every bit of acclaim it's gotten. Also, I love that the Hawaiian history aspect of the film. We forget that Hawa'ii was a wonderful, perfectly capable nation before the American missionaries swept in (much like we did for many other places). I have a book on the last Hawaiian princess and to read how we went in and took their country from them breaks my heart. It's a beautiful world and the decision that Clooney's character made in the movie is one that I hope someone in the same position would make in reality.
So there's my mish-mosh opinion of it. I loved every last character, good and bad. Go see it. You'll be glad you did.