The largest problem with most image gallery scripts I've seen is design.... for I personally think they're all horrid. The text usually doesn't fit in, and the tables are laid out awkwardly, as if done by an amateurish web designer. And the price on most these scripts is ridiculous, despite their huge apparent flaws. Some are also designed way to simple (very basic features), yet priced quite expensively. You could probably pick up a PHP book and code a gallery yourself, to save the money.
Hopefully I can provide a solution to this, with the script I'm working on.