They picked very good directors for all 3 sequels, unfortunately Cameron was the only one who truly delivered on the potential. But I think perhaps the studio was to blame for the creative failure of the other 2. Certainly Fincher's movie.
Jeunet was forced to cut entire set pieces because there wasn't enough money allocated in the budget. I'd say that's a studio problem.
Plus there's Joss Whedon's script, which, as is usual for his style, depends a lot on dialogue. Jeunet was just learning English at the time, so its no surprise he couldn't realize that facet of the script (visually, the film looks amazing). On the other hand, Whedon's script has problems anyway, so I'm not sure a director with a better hand on the language could have done better.