I finished watching a little while ago, but since I'd already seen the finale, my whole approach to the season was very odd! I have to say, it's the first time I ever caught up with a show like this, DLing eps and watching them back to back, commercial-free, spoiler-free (well, apart from the whole "seeing the finale before most of the season" thing). On the one hand, I missed out on all the fandom chatter and fics while the series was going on. On the other hand, I had just a really pure watching experience. I didn't even know the synopses or titles of the next epi, just that it was the next ep.
My favorite eps are "Faith," (for being a little deeper, and having a girl Dean actually had chemistry with), "Hell House" (for bringing the scary AND the funny in huge doses, esp. the pranking!), "Dead Man's Blood," (sexy vamps!). Now seeing the finale with the whole weight of the season behind it and knowing who these characters are and what it means for Dean to question his dad? Yeah. Huge deal.
Worst eps: Definitely "Phantom Traveler" and "Route 666." That actress who played Cassie? About as good an actress as the girl who played Eve on "Angel." Srsly.
Pics in no particular order. Very Dean-centric. ;-D)