Smallville season 5 has 22 episodes.
1) Arrival
As the Fortress of Solitude rises Lana meets some otherworldly visitors with Kryptonian powers. Jor-El begins revealing some of his true plan which involves saving the planet even if it calls for the sacrifice of a few. Lionel is zombified and knows an awful lot about Zod’s disciples.
-It's an exciting episode. It's a reminder that, yes, you are most definitely watching a comic book-based show, but hopefully that's a good thing.
2) Mortal
This time it’s Lionel in Smallville Asylum. Lex knows there’s something in his father that could bear amazing revelations and is maddened at not being able to get to it. While Lionel is alien-influenced Clark is completely normal which is bad news when 3 villains escape from Lionel’s institution and force a non-super-powered Clark to pull a heist for them. Clark and Chloe team up only to find far more than they expected to.
-Chloe's uber-resourcefulness is a little far-fetched, but then again so are Clark's super powers. The powers of the villains add some visual flash to this episode with no Superman powers. Despite that lack, though, it's a really good episode.
3) Hidden
Chloe’s friend has intentions of blowing Smallville off the map to "save the world" from the meteor freaks there. A still mortal Clark teams up with Chloe once again to find and stop the maniac. Clark gets his powers back at a price that he can’t live with.
-I thought the villain and his ties to Chloe could have been better, but there's some strong emotion in this one which makes for a good episode.
4) Aqua
There’s a new guy in town, an aqua man, and Lois is falling for him. Something is killing fish in the area and Aquaman is feeling their pain. Clark sees the vigilante action and sets out to stop A.C. only to find he can do a lot more than swim fast.
-It's great to get another super hero in the mix.
5) Thirst
Chloe gets slapped in the face by the Daily Planet and is in need of a story. When Lana starts acting strangely after joining an elite sorority Chloe finds herself in the middle of a story more likely to show up in a tabloid. Clark finds himself in the position of victim rather than hero this time. Lex and Fine face off with Lex finding that despite the other man only being a college professor, he’s more than a match for a Luthor.
-It's a cheesy-dark episode befitting of Buffy the Vampire Slayer (with plenty of references to the other show). But while it might not be the strongest dramatically it's still a fun episode and sets up Chloe in the Daily Planet.
-Carrie Fisher has a small role.
6) Exposed
Chloe and Lois witness a murder and set out to uncover the story requiring one of them to pose as a stripper. The victim is linked to Jonathan’s senatorial friend, and Clark sets out to clear the man’s name thinking that this is Lex’s dirty way of winning his own bid for election to the Senate. Clark learns some hard lessons in the nature of humanity and political justice.
-Tom Wopat plays a sizable but unfortunately not recurring part with plenty of nods to The Dukes of Hazard.
7) Splinter
Clark is pricked by silver kryptonite and then is attacked. Clark begins having extreme paranoia even to the extent of attacking his parents. No one can stop him, and Lana is next on his list.
-Not the strongest episode just because there are so many other stories with outside influences changing a character's personality. It does further the Milton Fine part of the story, though.
8) Solitude
A flash of light leaves Martha on the ground, and Clark is worried that Jor-El is behind it intending to kill her because of what happened earlier. As Martha comes to the brink of death Clark turns to Fine for help and discovers some troubling things about his unearthly father.
9) Lexmas
Lex is shot while making a dirty deal to ruin Jonathan, Lex’s new opponent in the senatorial election. A near death experience shows Lex what his life could be like should he make all the right choices: a marriage to Lana with kids, a tight friendship with the Kents, and an estrangement from the Luthor family. Life is not all rosy, though, and Lex finds himself having to make difficult choices. Meanwhile, Clark is enlisted to deliver presents to needy kids and meets an unlikely helper.
-This is a more light-hearted and slightly cheesy Christmas episode (especially with the Clark playing Santa Claus bit), but it's enjoyable and is a good character moment for Lex.
10) Fanatic
Lois Lane assassin? With Jonathan as the target? Did Lex somehow manage to convince her to take out his rival for the Senate seat or is it the work of misguided fanatics? Meanwhile Clark’s personal fears put a kink in his relationship with Lana.
11) Lockdown
A home invasion leaves Lex trapped in his panic room. The maniacs outside are demanding the Kryptonian spaceship. As Clark and Lana try to patch things up Clark finds out about her secret studies of the ship with Lex. He’s upset at her not being forthcoming about it but has to face the fact that neither is he being completely honest.
-Some of this one feels rehashed, like Lex on the edge of death again, but it does serve to further the downfall of this little love triangle.
12) Reckoning
Clark decides that the only way to save his relationship with Lana is to come clean. He reveals all and proposes to her. This is the happiest day of his life until a devastating auto accident that he can’t reach in time. He turns to Jor-El for help but only one life can be saved.
-This is one of the signature episodes. It's touching and will affect the rest of the series.
13) Vengeance
Martha takes a trip to Metropolis where she is saved from thugs by a masked vigilante. Clark is determined to recover what the muggers stole. He finds himself turning to the vigilante for help and must decide if the best way to stop criminals is to finish them off for good.
-While I like the idea of Clark facing the decision of killing a criminal, this is perhaps the weakest episode this season. Vengeance is just not a gripping character. I like the idea of her back story, the murdered mom and all, but the Kryptonite-charged heart transplant as the source of her powers just doesn't work. The way she gets the upper hand on Clark is weak, too. What really kills it, though, is that the action looks cheesy. When Vengeance uses her powers it looks so obviously staged, not at all the level of quality I've come to expect after episodes like "Aqua" and "Run."
14) Tomb
The Talon is being haunted by a ghost. Either that or Chloe is flipping out. Is keeping Clark’s secret driving her to suicide? If so the psychiatrist is bound to uncover it, and with Lex involved that revelation could be even worse. If that weren’t enough trouble a serial killer has his eye on Lois.
-This is Smallville crossed with Stir of Echoes. It's a completely different approach to mixing in horror than "Thirst."
15) Cyborg
A bionic man escapes from his lab and runs into Lana then Clark. Should they get him back to the lab or help him get away? The decision becomes more difficult when Victor is damaged and in danger of death without repair. What is Lex’s role in all of this? Meanwhile, Martha is blackmailed for Clark’s secret.
-I didn't realize at first that this is the comic character Cyborg since this one looks like a normal human. Clark's x-ray of his machinery gives it away by showing the classic design just underneath the skin. It's a fun and touching episode.
16) Hypnotic
Clark is approached by a blonde with hypnotic powers. Under her spell he rips Lana’s heart out and spits on it. He’s ready to shun everyone he ever loved. Why is this happening to Clark? Nothing is coincidental in Smallville.
-This again feels like things we've seen before. It's red Kryptonite Clark approached from a different angle. It does serve to further the fate of the love triangle like the other one I mentioned.
17) Void
Lana is purposefully stopping her heart to reconnect with her parents in the afterlife. The drugs used for this trip are deadly dangerous and Lana is a certified junkie ready to steal to satisfy her need.
-It's apparently taken from Flatliners and an obvious excuse to give all the characters near death experiences. Still, those experiences are interesting. My one real complaint is that Lana goes from an emotionally distraught, thieving junkie to a well-balanced person in an instant. They should have stretched her underlying troubles over at least one other episode if not two.
18) Fragile
A troubled little girl can shatter glass with her mind. When mysteriously exploding glass kills her foster mother the Kents take the girl under their wing. Is this girl an unwitting killer? Upon learning her secret Clark has faith in her when no one else does.
-Side note: After a house full of glass violently explodes why is someone going to walk right up to an obviously vibrating mirror? The dialogue in the first part of the episode is stiff, too, but the episode improves further into it.
19) Mercy
Lionel is targeted by a psycho that likes to play lethal games. Lionel tries desperately to outsmart his attacker but is impressively outmatched. Now Martha is pulled into it. Clark, Chloe, and Lex team up to save them, but with Lex involved Clark is hindered.
-An obvious take off on Saw this is still a great character moment for Lionel. The guy that's the equivalent of Jigsaw is pretty unbelievable, but I found that forgivable with the other favorable aspects of the story. This would have been a great opportunity to introduce a new villainous mastermind - preferably a classic one. Someone of that caliber would have strengthened the story.
20) Fade
Clark saves a man’s life, but that turns out to be maybe not such a good thing. When the guy’s questionable morality begins to surface Clark rejects his gratitude and finds himself up against an invisible assassin. He also finds out that Lex and Lana are becoming more than just friends and doesn’t take it well. His attempts to protect Lana by hiding his secret may have pushed her into a relationship fraught with just as much if not more danger.
-Once again this is something we've seen before. Clark saves someone and that someone goes off to do bad things. He then questions whether or not he should just go around saving everyone that needs it. This story would have been stronger with an acknowledgment of the previous incident instead of acting like this is the first time Clark has ever considered this kind of thing. The whole invisible assassin thing is pretty cool, though.
21) Oracle
Jonathan tells Clark to kill Lionel. Could Lionel have secret plans to turn Clark into a weapon? What could be bad enough to turn Jonathan's heart so lethal? Lex is developing a super vaccine that he claims will benefit the world. Whose loyalties lie where?
22) Vessel
Lex is abducted by aliens, Kryptonians to be exact. Jor-El commands Clark to kill the vessel of Zod, which they figure is most likely Lex, before the Earth is destroyed. Clark has more problems than that to deal with when a computer virus completely shuts down Metropolis and riots ensue.
-Smallville does well with its season cliffhangers. This is an exciting episode.