The formality of the language one uses should match the formality of the situation and the relationship between the writer and reader. Consider the following examples.
Very Formal: Exceedingly large segments of the population are expressing their discontent with medical practitioners who appear to more engrossed in amassing financial assets than in providing efficacious care to people with health disorders.
Formal: A large number of consumers are complaining about medical doctors who are apparently more interested in making money than in provide effective health care.
Informal: A lot of people are unhappy with their doctors who only seem to care about how much money they make, and not about giving their patients good care.