Warning: There are spoilers in this summary, though not too many.
I was a big fan of Smallville Season 1 and 2, however, the show is seems to be wearing very thin. Season 3 had some absolutely AMAZING episodes... However, most of these amazing episodes all centered around the struggle between Lex and Lionel (his father). A couple episodes featured Clark kicking ass, and he developed more as a character, but for the most part, he's still a pretty two-dimensional character who has quite a bit of not-so-well-acted angst. I could also do without the endless romantic bout between Clark and Lana and some of the pain-inducingly-bad dialog between them.
Don't get me wrong, I still await each episode eagerly, though not as much as I used to (I'd much prefer to be watching 24 or Scrubs). Some of the show's appeal has just died off over time... Maybe it had something to do with the billioneth "Mutant of the Week" episode where someone gets infected by Kryptonite, gets powers, does bad things, hurts Lana/Chloe/Lex, and Clark comes to save the day. I wish the producers would just listen to their fanbase, and learn that the best Smallville episodes are inter-main-character struggles. For instance, my absolute favorite episode of Smallville is when Lex beings to get his memory back from the times his father had erased it, or when Clark learns more about his past. Basically, any episode furthering the Superman mythos, or any episode with lots of Lex and Lionel (the series' saving point, in my opinion).
There were definitely a few season-making episodes in this season. The first episode was a GREAT finish to the Season 2 finale, the episodes where lex is in Bell Reeve (sp?), and the episode when Lex gained some of his memories from his youth back. The episode where Clark and Dr. Swann talked was also very cool, as was the episode where Adam faced his bitter end, along with the episode where everyone was out to kill Chloe. There was also one "mutant" episode with a girl in a coma that "dragged' Clark into her dreamworld that was also VERY cool. The season finale, which aired earlier this week, also had a jaw-dropping end, though some of the dialog was simply down-right painful (the Lex/Lana airport scene comes to mind).
Overall, I just wish the producers would try to add more variety to the show. It's very possible to have an entertaining show without having some mutant trying to ruin the day. Overall, Season 3 was good due to a handful of remarkable episodes, but more than half the season was simply boring beyond reason. Just make sure you read a synopsis for each episode (one without spoilers) to figure out which episodes are worth watching. If anything revolves around Lana: run. Run very, very far away.