It's good news that you've taken on Lightbox to fix some of it's issues.
However, there are a couple of issues I noticed.
1. When a gallery has both portrait and landscape photos the portraits appear in the center of the screen (good) but the landscapes jump a few centimeters to the left (odd).
2. If a picture has a long description only 1 line is shown. The rest is truncated.
3. Minor point here: Is it possible to have the word 'Close' rather than the 'X' on the top right corner. On Lightbox 3 you could just click outside of the box to close it.
See all of the above on this link: