Johnston isn't a bad director, but I just don't think his movie 'fits' stylistically following the first two. A lot of the key elements are there, but the lighter atmosphere and horrible pacing hurt it a lot.
The performances brought it down as well, IMO. Sam Neill and Alessandro Nivola did okay. William H. Macy phoned it in, Tea Leoni was irritating, Trevor Morgan was even more irritating, and the mercenaries didn't really have room to be, well, anything. Laura Dern's cameo was a nice touch, though she came across a bit bland as well.
The absence of John Williams didn't help, either.