I don't think he did anything wrong at all. Even the timing of his leaving was surely designed as a very loud wake up call to Mr. Lerner. Although, come to think of it, Randy himself did a fantastic job too, so you have to wonder what all the recent fuss has been about.
If O'Neill had a fault, it was generosity: giving all those young and untried players their big chance in Europe; fixing it for Mrs. Heskey's little boy to get to play with a real professional football team; all those really quite high fees and wages for - some might say - mediocre players. Yes, he was Villa's Willy Wonka was Martin and, let's not forget - he never relegated us! Not once!