A lot goes down for Sam and Dean in season 5. The story line, in my opinion, has gotten pretty heavy and I am ready to get back to the hunts. This season gives you an idea that maybe that is the direction they are going. I have not seen any of season six, so I am not sure if this sets up for less Demon/Angel stuff, or more.
I loved the first 3 seasons of this show, and liked season 4 & 5. I have a feeling though, if I had started watching during season 4 or later, I would have thought, "Supernatural Soap Opera. No thanks." I won't give to much away, but note that Sam still has a lot of inner struggles, Dean still likes women and his car, Bobby will still be calling them idgets, and Cass ALMOST starts getting jokes...sort of. The more I watch of this show, the more I love Bobby and Cass. If you watch this season, you will witness Cass trying to set up his voice mail (I was rolling with laughter) and Bobby has to kiss a man. I wont say why or how, but it was also funny.
The end of this season is pretty fast paced and will leave you going, "What? Really? What NOW!?!" It isn't the cliff hanger that is normal for the last episode on these seasons, but definitely lets you know there is more to come.
I hope this helps. I didn't want to just explain what happens, you can read the synopsis for that. I just wanted to give you an idea of what to expect as a fan. Plenty of laughter, lots of action, and actually, you may cry in one episode. Maybe 2.
Thanks! God Bless!