I think it was one of the better big pharma M&A moves in the last several years (ie, Pfizer/Wyeth, Merck/S.Plough). Genzyme is a productive company, making $400+million a year with the real prospect of Campath opening a $3.4 Billion dollar market. Personalized medicine is getting bigger and bigger every day and rare disease treatment is super high yeild protected nitche market (ie. Alexion Pharmaceutical).
Saying that it was one of the better big pharma M&As of recent years is like saying a short hemorrhoid is better than a long, dangling one.
Genzyme is a company that has seen its peak. It once had the enzyme replacement market all to its self. It now has increasing competition and is losing market share in no small part due to its manufacturing problems.
The Campath sales forecasts, making the large assumption of its approval, are pure fantasy. Even the dense Viehbacher realized this as he attached CVR to it rather than taking Genzme's word.