1. This is the season that brought me back to the show after I lost track of it back in s2. "Ask Jeeves" convinced me to purchase a season pass, and after that I quickly snarfed up the previous 9 seasons (all out of order). Even if the rest of the season disappointed, I'd love it just for that alone.
2. But the rest of the season didn't disappoint. Not to say I adored every episode, but I dearly love a pretty sizeable chunk of them: "Fan Fiction", "Ask Jeeves", "Girls, Girls, Girls", "Hibbing 911", "About a Boy", "Halt & Catch Fire", "The Things They Carried", "Inside Man", "Book of the Damned", "The Werther Project", "Angel Heart".
3. I probably watched "Ask Jeeves" and "The Werther Project" about 8 times each while waiting for the following episodes.
4. I know fandom was (and is) divided over the character of Cole, but I thought his whole little arc was interesting and satisfying--if only because it's one of the rare occasions we get to see Dean go all-out against a normal human. (Also, his last episode, "The Things They Carried" has some ridiculously beautiful shots in it.)
5. This season gave us the marvelous addition of Rowena, who definitely stands as one of my favorite recurring characters. In this season in particular she's magnificantly amoral.
6. The overall season arc of Dean and Sam coping with all the various issues arising from the Mark of Cain is pretty compelling--and I loved that unlike s3, Sam has the chance to actually act on his reckless desperation, and then succeeds. And then the next season is spent dealing with the consequences, sure, but I thought it was a good way to mix up the partial thematic retread of an earlier season.
7. Crowley talking with a hamster:
What are your favorite parts of s10?