This is by no means the best Smallville finale. In fact if I had to rank it, I'd say it's probably tied for the 2nd weakest finale with season 1, but still light years ahead of he awful season 8 finale. One real problem is that nothing truly exciting happens for 3/4 of the episode. A Smallville finale should be non stop excitement, with plenty of twists. There are virtually no twists in the entire episode, and as I already said, the excitement comes way too late in the episode to be satisfying.
There are some highlights here. Kara and Brainiac are used very effectively.. Also, while many people didn't like the way Lex was written out, I loved how his character developed up to this point, and the final scene between him and Clark was pleasantly subtle.
Unlike the season 8 finale, this episode I believe is partly excused for being a bit of a disappointment. For one, the writers strike did more than shorten the episode count from 22 to 20 this year. Nobody knew when it would end, so as a back up plan the producers had to plan on an early finale with "Veritas". By the time the writers strike had ended, they had already made some plans that had to be completely rearranged. I've already said before in my comments on "Veritas" that it feels like the finale would have been much better as one episode. If they had been able to plan a full season without any complications, and the scenes that made up in Veritas, Descent and Arctic were to have been combined, that would have made a fantastic finale. One also has to consider that this was the finale season for show creators Gough and Millar. It's clear they were either suffering from Smallville burnout or writers block, which can happen after 7 years on one project.
I don't want to make it seem like this was a terrible episode. As a mid season story, this would have worked very well. As a finale, it's hard to deny that it falls short.