I wouldn't go as far as to say evil! basically, the Daily Mail is a tabloid, like any other. It's style is sensationalist, often at the expense of the facts and it's contents tend to be orientated around popular culture, rather than more serious issues.
The Sun, Star and Mirror are targeted at the lower end of the market, whereas the Daily Mail and the Express cater for the slightly less "chav" variety of "average Joes".
Consequently, the Mail likes to consider itself respectable, but accessible, although it is just as poor in terms of journalistic merit as the Sun. Traditionally, the Mail has always been the paper of the tory - although New Labour types have somewhat blurred these boundaries and of the major nationals, only the Guardian maintains any pretence of having left wing sympathies.
This has lead to a readership of Royal loving, middle aged, lower middle class types of below average intelligence who are interested in Cliff Richard and Cilla Black's lives rather than any actual news. These people are very set in their ways and believe that what they read in their daily newspaper must be true - they're old enough to remember a more innocent time than the one we live in now.
So when the Mail prints a libelous story, there's a lot of fifty somethings out there who will swear it to be true until the day they die. Which is why the Mail has become the butt of jokes lately.