First 1/3 of the movie are nearly 5-star perfect. The exposition and case statement/dilemma for Kal-El are beautifully set up, acted and scored. Reminded me of a Terence Malick film.
Unfortunately, the wheels come off for the last 2/3 of movie. The story, acting, and direction for the last hour are so uneven and obviously slapped together in post-production but I'm tempted to say they might still have a perfect movie laying on the cutting room floor. The effects are layered on too thick, the fight sequences go on too long, and the characters lose all emotional resonance under the weight of all this effect mayhem.
Do yourself a favor and leave after he discovers the Kryptonian Scout ship in Canada, then wait and see if they get it right in the sequel.