8) Breaking Bad
Breaking Bad is a prime example of a show that that could have turned out hugely differently if some early ideas were followed through. In this case, it would have certainly affected the series for the worse.
Though it was never what creator Vince Gilligan wanted, various execs from different studios he pitched the idea to wanted to replace the meth angle with something much lighter, with one suggesting that Walter could launder money. Infamously, AMC initially offered the role to Matthew Broderick, as well as John Cusack, before Bryan Cranston was cast.
Another big change almost happened at the end of season one, when Jesse was to have died at the hands of Tuco. Instead, Gilligan had No-Doze die instead, because he realized that Aaron Paul – who was initially turned down in the role for being too good-looking to play a drug addict – could do a lot more with the part.