I agree, the Lana/Witch storyline was a stinker. I pretty much almost called it quits too. But the season finale was so awesome, the Fortress of Solitude!!!!
But SMALLVILLE has always been an up and down show in quality and pay off. And everytime I thought I was done with the series, (read with Al Pacino voice) they would do something that would drag me back in!!!
I LOVE SUPERMAN!!! He is my number two Hero, right after The Bionic Man!
But I actually grew to enjoy many aspects of Smallville unique, separate continuity from the established comics. As the show went on, in many ways it became a series not just about the journey of Clark but about the Birth of the DC Universe.
The best part of Season 5 was the introduction of Brainiac, I thought that was well done. And season ender with Lex possessed by Zod was pretty epic by Smallville standards. I hated the idea of Jor-el killing Pa Kent. AI or not, that does not jive with the Jor-el I know. And I think the writers realized their mistake in this regard, as they definitely attempted retro-con Jor-el into a more supporting role in later seasons.
Season 6 is cool with the introduction of Green Arrow (essentially fullfilling the Superman/Batman relationship from the comics), rise of the Justice League, the hunting of the Phantoms, and I really like the Lex/Lana romance. (my brother-inlaw was married in the exact same church a year later, I kept looking around for Lex to show up. LOL!) I just wish Lex had really killed Lana, I think that would have been very dramatic.
Season 7 was a mixed bag, affected by the writer's strike. The introduction of Supergirl I had mixed emotions about. I loved Bizzaro! The Veritas subplot I don't really think paid off, though it was an interesting idea. I still to this day do not understand the season finale... Lex destroys the Fortress and kills himself? What was suppose to happen? How was the device suppose to control the Traveller??? For a final confrontation between Lex and Clark, I found it very disappointing.
Season 8 and DOOMSDAY. A little uneven, but I really enjoyed this season. I even liked the final showdown, however brief it was. Tess Mercer was a breath of fresh air, I really liked her. Plus the Legion of Superheroes!!! Though I absolutely hated the return of Lana! Lame! She is worse than any kryptonite.
Season 9 Zod and the Kandorian clones! A very solid season in my opinion. Though why they did not bring Supergirl back for an arc I still don't understand. But seeing Jor-el in the clone flesh and our first real look at Krypton before its fall was excellent! And the JSA episode was one of the best of the entire series!
Season 10.... I may be in the minority, but I LOVED the final season. Sure, maybe the overall DARKSIED arc did not pay off as we wanted (but that is Smallville for you), but I completely enjoyed all the small moments, all the comic book and Donner nods and the romance between Clark and Lois was perfect.
As for the question about budget. Yes, the look of the show definitely began to change after seasons 6 or 7, less and less exteriors/on location shooting, more and more set pieces... and the reason for this is standard tv practice. The budget remains pretty much unchanged over the course of 10 years but the salaries and production costs go up and up and up with each new season, thus you get less bang for you buck on the screen.
I have actually begun rewatching my Smallville sets, taking notes for a future planned Superman edit, and show still shines and captures the viewer.
I think it will be looked back as a classic genre show. I definitely think it will stand the test of time better than LOIS & CLARK does.