Even the most ______ critics had to admit that the artist's latest exhibition, a vibrant collection of abstract sculptures, was a powerful and thought-provoking display.

✓ Correct Answer: Option C

The phrase 'Even the most ______ critics had to admit' implies that these critics would typically not praise the artist. Therefore, 'disparaging' (expressing the opinion that something is of little worth; derogatory) fits, indicating critics who usually find fault.