The phrase "left no stone unturned" suggests thoroughness and completeness in the process of searching, investigating or exploring. However, there are several antonyms possible that indicate a lack of thoroughness, incompleteness or disregard for details. For instance, one could say "left many stones unturned," "did not give it my all," "was only surface-level" or "skimmed the surface." Alternatively, someone might say "made only a cursory effort," "skipped over many details" or "failed to exhaust all options." These antonyms suggest a less comprehensive approach to the task at hand, indicating that there may be areas left unexplored or overlooked.