The opposite of flawless can be described using several antonyms, including:

• Imperfect: This suggests that something is not flawless or ideal.
• Blemished: This refers to something that has marks or flaws that detract from its quality.
• Defective: This means that something is faulty or incomplete.
• Flawed: This means that something has a problem or shortcoming that makes it less than perfect.
• Bad: This suggests that something is of poor quality or not desirable.

Other antonyms for flawless include inconsistent, amiss, unsound, weak, deformed, and fallacious.