This userscript applies to metal-archives.com(Metal Archives), in the Review section.

As per request here: Improving the Display of the Review Section

The script:

• groups all reviews for the same album in one entry,
• changes the relevant value in the Authors column to e.g. (2 authors),
• replaces the Rating percentage of the entries, with the average of them all,
• updates the entries count of the displayed Review entries list (i.e. after removing the duplicate entries)
  to the navigation buttons located to the start and to the end of the list, and
• works when changing Review pages or after switching the pages 'tabs' (DATE, RATING, ALPHA).

Screenshots
Before:

After:

Tested in Greasemonkey.