Man in Black III still has the action, humor and suspense. I love how they made the plot work and it related to the previous Men in Black movies. It had the right amount of action. It had less humor but its still good.
The movie unravels more of both Agent J played excellently by Will Smith and Agent K. Although I still think that the Smith and Jones pairing is the best, Young Agent K starred by Josh Brolin portrayed an interesting character too.
As for the 3D, it was totally unnecessary for the movie. I felt like watching I was watching it in 2D although it was in 3D for the whole duration of the movie. It didn't affect the sensation of watching it.
Bottomline, I suggest you watch this movie. It's worth the watch especially if you've missed the Men in Black in action. But if you want to save some bucks, better go with just 2D.
Watch Men in Black III!!!