I'm not trying to be a smartass, and maybe this has been asked before, but I don't understand how episode quality or main actor appearances has anything to do with the ratings.
IIRC, the only character who's presence has an effect on the ratings is Clark. Clark-centric episodes, which often happen to also be mythology-heavy episodes, have done pretty well. Episodes focused on Lex, Lana, Chloe, Lois or Jimmy - not so much.
Of course, other factors like episode scheduling (
Lexmas was under-promoted and shown between a ton of repeats) preemptions in certain markets (which I think hit
Progeny) and competition are important IMO. I think a big reason for the solid ratings in the beginning of the season was scheduling ten episodes in a row. The seemingly random pattern of new and repeat episodes, especially in the spring, kills a lot of
Smallville's momentum, IMO... and gives me more time to think about how badly the crack monkeys are screwing things up.
Wouldn't the episode *afterwards* have more bearing on episode quality than the episode itself? (I'm not counting premiers and heavily-promoted comics episodes and guest stars.)
There are a lot of factors involved, but this is on I personally like. My favorite example of what I like to call the "Salt the Earth!" theory is the 500,000 viewer drop between
Promise and
Combat. The retcons and OOC behavior were so bad that a half million viewers left, and
never came back.
Promise started a downward spiral of ratings that only started to turn around with
Phantom, the season six finale.
OTOH, well promoted episodes with DC comics character often do really well -
Run,
Aqua,
Cyborg and
Arrow were all strong, IIRC, and
Justice was the best rated episode of
Smallville ever.
Of course, to get around this the promo monkeys do things like make deceptive promos (
Static showed almost every Clark scene in the episode, while avoiding the Lexana A-Plot) or just flat out lying about episode content (Lois in promos for
Abyss,
Legion and
Bulletproof.) Bad promo monkeys!
A check after an episode like Sleeper or Stride/Hero (not Promise because it had a hiatus before Combat)
According to
Omar's reviews,
Promise aired 3/15/07, and
Combat aired 3/22/07.