One of my favorite series ever, it's damn funny. A little teenie bopperish in the very beginning and then it drags on in much later seasons. But they really grow as actors...Well, Dean does. Sam not as much.
Probably the best thing they do well for quite few seasons is mix in the primary plot line, random monster hunts, and other nonsense/humor so it's not always the same thing episode after episode. It can jump around and it keeps it a little fresher when you consider there are 22 episodes for 17 seasons.
You're 2 or 3 seasons away, but I'm saying it right now. I defy you to not LOL at the episode, "Mystery Spot".