That's the problem with having a 22 episode season. It's why network shows end up with filler episodes. Your stronger cable shows always have 12-14 episodes and the shows end up the stronger for it. This coming up ep is a mytharc episode, and a strong one according to that review by Alice Jester that I linked upthread. Othello, I'm sorry you've been disappointed, but I doubt Supernatural will end up like the monstrosity that was the BSG series finale. I hated that, too. Very little in the finale satisfied me, and the coda at the end just ticked me off no end.
I've often wished that SPN were a cable series so that it could push the envelope much farther and be only 13 eps a season. SPN is by far my favorite network show, but the writing would be much tighter were it airing on HBO, Showtime, or even FX like Damages or The Shield. My favorite overall show is a tie between Dexter and Mad Men, both only 13 eps a season. SPN's greatest strength, IMO, is its character work. I like the Lucifer story, but it's being delayed because networks have to stretch it out to accomodate the 22 episode schedule. This last week, while sweet, was filler. The upcoming eppy isn't.