This tenth and final season is one of the best of the series, as engaging as it was the first few years it was on "The WB". It begins with Lois knowing Clark's secret, that he's the superhero known as "The Blur". She goes away on assignment to Egypt for a while, where she runs into Carter Hall, who is Hawkman. Clark's Kryptonian cousan, Kara, returns to Earth and warns him of an impending danger. This turns out to be Darkseid and the World of Apokolips. Rather than being actual beings, they are more like those creatures from the Phantom Zone that possess people and take over their bodies. However, everyone who is contaminated by this evil has this weird "Omega" symbol on their skull. Some of these people are the ones in charge of passing the new "Vigilante Registration Law", which wants to keep tabs on these people with superhuman abilities.
Tess Mercer, who runs Luther Corp, looks after the clone of Lex that is found--and it's eventually discovered that he's actually a clone of both Lex and Clark. He's invulnerable. This is a nod to the "Superboy" character. A reformed Braniac (James Marsters) appears in an episode in which Clark attends his High school reunion. And there's also a few "Parallel Universe" stories in which he's transported to a world where Lionel Luthor, not the Kents, had raised him. And these alternate personas--Lionel and evil Clark, make it to our world and Clark has to deal with them. There's also the return of Return of Zod, who was banished to the Phantom Zone the previous season. Since this had really been a younger clone, his disembodied spirit which was already there (from the original Zod, banished by Jor-El) reunites with it, basically resurrecting one of Superman's main villains in years to come.
The story with Tess is tied up, with her dealing with the Luthor legacy--and discovering that Lex Luthor (Michael Rosenbaum, returning after a few seasons) has managed to piece himself together with bits and pieces of all the different clone he's had growing. The only thing he needs is a heart that is compatible--and since she's his half-sister she's the likely donor.
The two hour season finale is satisfying and sets up the Superman scenario well. When he finally gets all his powers from the Jor-el and the Fortress of Solitude, he's many times more powerful which is all shown from long-shots and has a computer animated Superman flying in the sky and physically moving the planet of Apokolips away from the Earth. He's even able to survive in outer space. By the end of the episode, and the series, Clark Kent/Superman is set up to be the character we know him as. Recommended, even if you haven't seen SMALLVILLE in a long while.