There were some subtle changes to the origin story which keeps the story fresh. New/different Krypton than we're used to but they add a new perspective to Kal-el's motivation. I also liked the new angle given to the relationship between Clark and Jonathan Kent.
Beyond the story, the FX and action are just about non-stop. My one complaint with the Superman story over the years is the silly notion that by simply putting on a pair of glasses no one realized that Clark Kent and Superman were the same man. Man of Steel puts that joke to rest, which alone makes it worth seeing.
This movie benefits more than most from an IMAX screening. 3D is fun but not necessary for a good time.