I like the lightbox, but you might have some issues. Firewalls, browser settings and browser extensions like Adblock Plus, NoScript, Flash Block, Ghostery, etc. can all affect lightboxes.
You should test the a page or two on the most common browsers that visitors to your site use (pull from Google Analytics). If you don't see any issues and your target audience isn't inclined to use extensions you should roll with them if you like their look and feel.