Absolutely amazing series filled with emotional ups and downs. Happy and sad cried so many times at this show. (This prior statement is only in relation up to season 3)
Season 4 is overtly religious.
**SPOILER BELOW**
However, a good fiction needs to allow the audience to "suspend their disbelief" and season 4 becomes extremely religiously preachy with one of the characters meeting god.
As an atheist this completely took away my disbelief. It's a series that is supposed to be set roughly in the real world; I could no longer believe in the this world and lost the emotional attachment.
As an aside; I had no issues with the characters religious feelings prior to this. His personal journey of being religious and his personal life conflicting with his church's beliefs was touching and endearing. I was actually hoping he managed to consolidate both parts of himself. However, I don't think religion should be pushed down anyone's throat.