I think I pretty much agree with your assessment.
Season 8 is my favourite season. As a big Cas/Misha fan at first I found it weird, because Misha is still only 'special guest star' and Cas is not in that many episodes. But then I think having Benny in it and two Charlie episodes made up for that. And like you said it's the steady goodness of it. Some eps hit higher notes than others, some eps I don't like much, but it's less than with many other seasons. Also I'm not really interested in the Amelia storyline (I don't hate her, like at all, but it's relatively boring to me), but then the Purgatory flashbacks really make up for that.
From my shipper perspective the destiel of the season is flavoured so beautifully angsty and we also got the deanbenny XD So I'm happy on that front too.
Maybe s8 also stands out even more because s7 was such a dip for me, but idk I really love it.