I enjoyed it. The story was a bit predictable, but not overbearing. The effects were VERY well done, and never stood out as "Look at me!" The 3D was good, not overdone, and didn't give as bad a headache as normal.
One glaring error throughout, though. You cannot fire a bow with your fingers on the same side as the arrow. Although Cameron would never get away with showing people constantly firing pistols with no clips in them, he gets away with this because people don't know archery any more.
Of course, it won't matter to most people, but it's another example of "Oh, well, it looks cool, and no one will know the difference." That's the only reason I didn't give it 5 stars.