Possible Clues:

• Perhaps unflattering review of small exhibition is unfair? (3,4,2,4,2)
• Plain situation requiring a microscope? (3,4,2,4,2)
• Visually uninspiring
• Plain lot to touch a monk unexpectedly (3,4,2,4,2)
• What one with poor prospects has — that's plain (3,4,2,4,2)
• Little scenery and it's fairly unattractive (3,4,2,4,2)
• Hardly a knockout
• Quite plain there's little to watch on TV
• Unprepossessing, like a small portion
• Little in prospect? That's plain (3,4,2,4,2)