I have been rewatching some of the Smallville episodes on TNT (they run quite frequently). I did not watch the show during its initial run.
In my opinion, the show did an almost reverse "jump the shark" move (only know 1 other show that did this).
1) The Early years - there were the early episodes that centers around Smallville, Clark, Lana, Cloe, brooding Lex, and which almost every single problen was derived from the Meteors. Most of these episodes bore me to death.
2) Oliver Queen's addition - Lana gone, Locations moves from Smallville, larger suport case, more "supers", introduction of Lois, some global intrigue, etc. I find these episodes so much more fun and I relaly liked the Oliver character.
There probably was a middle period where Lana and Lex were kind of on their way out and the series was trying to find its footing (gradually improving).
anyway, that's my take would be interested in hearing other people's feelings.
I though that the actor that portrayed young Clark did a really nice job, in fact, I would have much more preferred Superman Returns to actually have used Tom Weiling as the new Superman, launching him from TV to Movies!
He had a feel for Supes, and had a built in quite large fan base to take with to the Movies!
Also think the actor that did lex would have been much better suited than current one chosen, and could also use that actress who played Kara to hit movies running with!