Asylum and Murder House are the best season by far, IMHO. The other seasons try but don't come close. What they tend to lack is a compelling story line. It sometimes feels like they make it up as they're going along. Many of the seasons are intertwined, but not so much that you can't follow.
Every season is visually impressive, but then they go off on a tangent, drop characters, add in plot lines out of nowhere, etc. I usually end every season with a "wha???"
That's my 2 cents. I like the show, but I don't know if I'd call it "can't miss tv."