Expresses an extreme state or condition; translated as 'to the utmost', 'extremely', 'as can be'.
Long explanation:
The ~限りだ grammar point is used to express an extreme state or exclamation. It emphasizes what precedes it, indicating an exceedingly high level or degree of that particular state or condition. It is extremely idiomatic, usually translating 'to the utmost' or 'as...as can be' in English.