For me, the point of no complete return came in 3.2, when Lana KILLED a guy and it was never mentioned again. Clark accidentally killing is one thing; he has a different perspective on life, but it should have had an effect on Lana. Some good eps followed, including Memoria (the series' single best, as far as I know), but they had an elegiac quality to them; it was clear to me that the show was no longer interested in reconciling the comic book mythos with reality (we only saw one classroom in the first three years), and without that crucial balancing act, I wasn't interested. Legacy should have been great, but barely made sense. The S3 finale was decent enough, but though I may watch 4.1 one day just to see how it ends (I've read the spoilers), I wasn't invested enough to continue. Maybe I'll watch some of the better-reviewed S8s one day, but the emotionally rich and tantalizingly realistic show I'd identified with (I was a high school sophomore during S1, and, like Clark, had an impossible crush) died in 3.2.