I'm not one of the gloom & doom people when Sera took over that thought the sky was falling... but I think this is probably good for the show.
I look to Smallville... The original showrunners had a good idea where they wanted to go, they went there, and then they left. The replacement runners had episodes all over the map from great to meh... and nothing had the focus of the original theme.
Supernatural had a very clear arc that was carried through... I like Supernatural, and unless someone has a great idea for another mega-arc... I think the show might be served better IF it brings in new blood every season or two and keeps the show fresh until its eventual ending.
Yeah baby! It's Halloween!