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New York Times:
Somehow, Mr. Dreyfuss maintains his sound comic timing even when Frank Oz's antic direction calls for hand-waving hysteria.
This cruel but effective black comedy violates credibility at almost every turn, but the concept itself is so strong hat it winds up working pretty well anyway.
Murray, with his curious blend of pathos and aggressiveness, is terrific, and so is an acutely uptight Dreyfuss, never once copping a plea for our sympathy.
With Dreyfuss and Murray on top form, not even the familiar plotline -- uptight rich person meets free-wheeling poor person and learns about life -- can prevent this lunatic comedy from being funny.
Bill Murray finds a real showcase for his oft-shackled talent in this manic comedy.
With his twisted lower lip, doleful eyes and trademark deadpan, [Murray] exudes an awkward -- and funny -- vulnerability.
Above all else, What About Bob? addresses the way many a patient feels when his psychiatrist has the nerve to go away without giving a thought to his problems. Perhaps it is just one desperate cosmic cry for help. Then again, maybe it's a threat.