I haven't read through the thread, because I imagine there are spoilers. A buddy and I just started watching it on Netflix. He has more free time, so he finished the series. I'm coming up on the end of season 4.
Some random thoughts so far:
I love how they handled the idea of a prophet.
Loved the "Groundhog Day" episode.
Can't stand the new Ruby. First was much better. (Sorry Mr. Padalecki, if you're reading this, but your wife can't act).
I also preferred the first Alistair. Second one is too... Statham.
I don't like the direction that Sam is heading, but I prefer it to the "But let's fiiind Daaaaad!" wuss.
Also, there are two moments from the series that really creeped me out.
The neck-slicing girl from the painting.
The faces that everyone sees when the hellhounds come to take them.
Oh, and the demon girl from Battle Royale was pretty fucked up, too.