Seeing the same thing on all 2.0.x versions including 2.0.11. Thousands of these queries per page:
SELECT image_slug FROM xxx_ngg_pictures WHERE image_slug = 'image-443' AND NOT pid = 0 LIMIT 1
Each page takes several tens of seconds per load, and sites with a larger number of photos take significantly longer.
This only appears to happen with galleries created *after* the upgrade, however. Galleries created prior to v2.0 still load fine. This is happening consistently on multiple sites running the plugin.
Reverting to 1.9.13 fixes this problem.