NextGen has been my go-to gallery for WordPress for quite a long time. Very easy to use for my clients, and super-easy to customize. But the included lightbox scripts are not so great-looking.
I recently started using Easy FancyBox to replace those scripts. If you go to Options > Effects under NextGen and select ‘none’ for the JS Thumbnail effect, you can then tweak Easy FancyBox under Settings > Media. It looks great right out of the box (so to speak) and has some nice options for fades and titles.
Here’s an example of NextGen with Easy FancyBox from a recent project.