Smallville season 4 contains 22 episodes.
1) Crusade
Clark is missing and Chloe is presumed dead. Her cousin Lois is out to find out what happened when she runs across Clark naked in a field. Clark is not himself at all having instead the mind of Kal El the Kryptonian enforcer. Jonathan is brain dead, and Lana is living it up in Paris with her new guy.
-Whatever weaknesses I may see in the season, it starts off quite well.
-Margot Kidder (Lois Lane from the 70’s-80’s movies) puts in an appearance.
2) Gone
Lois and Clark investigate what happened to Chloe when they are set upon by soldiers. Lionel prepares for his day in court and draws the battle lines with Lex. Lana, possessed by the spirit of a witch, is drawn to the Smallville caves. Lois proves she is not going to be a damsel in distress always in need of saving.
-Michael Ironside is General Lane.
3) Façade
An unattractive girl has an experimental treatment that leaves her beautiful but with unexpected and undesirable abilities leading Lois to start her first investigative report. Lana’s boyfriend is the new school assistant coach, Martha takes over the Talon, and Clark tries out for the football team.
-Eric Johnson reprises his role of Whitney. Michael Ironside puts in one more appearance as the General.
4) Devoted
The school's cheerleaders are handing out love potions to unsuspecting boyfriends on the football team. The problem is the side-effect of homicidal jealousy. Now one of the girls has her eye on Clark but so does a doused Chloe.
-A little cheesy, but kind of fun at the same time. It brings in some extra tension with Jason and Clark.
5) Run
A super-powered guy that’s not Clark saves Jonathan from being run down – while stealing his wallet at the same time. Bart moves like a flash, even faster than Clark, but has chosen to live a dishonest life on the streets. Clark has seen the good in him and wants to convince him to straighten out.
-A very fun episode. This as much as any episode I can think of thus far displays the special effects improvements since season 1.
6) Transference
Lionel finds a way to swap consciousness with another person. He goes for Lex, but Clark steps in and becomes the victim. Clark, trapped in prison, searches for answers while Lionel tries out Clark’s powers and life.
-Nice acting by Tom and really impressive stuff by John (who's almost unfailingly great anyway) as they completely change characters. Margot Kidder puts in one more appearance.
7) Jinx
Mxyzptlk can cause things to happen just by thinking about them. When Chloe and Clark realize he’s using superhuman powers to manipulate events so he can win bets the villain shows them that a knife is also an effective manipulation tool.
-Not as explosive an episode as I expected for the rarity of a classic villain, but still one of the best of the season.
8) Spell
Lana discovers that her ancestor was burned as a witch. Lana finds her spell book and tries to uncover the mystery of what happened. Now the spirit of Isobel has fully possessed her and intends to raise her sisters in the bodies of Chloe and Lois. The three plan to seek the Kryptonian stones, and Clark quickly finds that he can’t take magic lightly.
-It's like Charmed meets Superman. I expected to dislike this episode since I'm not fond of the witch story-arc in general, but taken as a self-contained story it works better.
9) Bound
Lex hooks up with a gorgeous girl at a party only to wake up next to her bloody corpse in the morning. Lex looks guilty, and even if murder is not his crime, Clark sees a disturbing dark side in his friend. Lionel claims to have turned over a new leaf and offers to help Clark help Lex.
-While there is some cheese at the end, this is a slightly more mature story than most this season. It could have been improved by a slower and more subtle reveal of the villain, but the mysterious elements work better than many similarly set up Smallville episodes.
10) Scare
A Luthorcorp accident releases a chemical that causes people to fall into a sleep state riddled with nightmares. The state of constant fright eventually wears out the hearts of the victims. Clark and Lex must find a cure before the whole town dies.
-In some ways an unremarkable episode, but I love the creepy dream moments especially with Chloe.
11) Unsafe
Alicia is deemed cured and released from her institution. Clark decides to give her another chance, but Alicia takes it too far, dousing him with red Kryptonite to get him to marry her. Meanwhile, Lionel pledges to make the world a better place, but nobody believes him.
-I didn't expect to see Alicia again and was a little impressed with the direction it ultimately goes. The tension between Clark with his relationship with Alicia and his group of friends, especially Lana, would have been something interesting to see spread out over more episodes.
12) Pariah
Nobody takes well to Clark and Alicia having any kind of relationship. An attempt on Lana’s life looks like the work of Alicia. Clark puts his neck on the line for her but is less and less convinced that she’s innocent. Alicia thinks their life together would be easier if he would reveal his powers to the world and engineers a revealing moment with Chloe who she thinks will print the information in her paper.
-I think Clark got off the hook a little too easily after the last episode. It would have been more interesting to have him have to deal with the marriage especially in the light of what ultimately happens between him and Alicia. I also think that there should have been more time between her violation of his trust AGAIN last episode and his willingness to stand up for her initially in this one. “Devoted” and maybe “Facade” could have worked great in between these two episodes with Alicia added to the others. On the whole, though, this is a great episode with some nice emotion on Tom's part. I also really like what happens with Chloe, and the reveal scene that kicks it off is great, one of my favorites of the series, actually.
13) Recruit
Lois kicks the crap out of a drunk college guy that won’t leave her be. When he ends up in the hospital paralyzed the next morning Lois is arrested. She and Chloe set out to clear her name. Clark is being recruited by the same college, and their resident football hero, also from Smallville, shows Clark what it’s like to be under the constant pressure to use superhuman powers on the football field. Meanwhile, Lex and Jason discuss researching Isobel and unraveling the mystery of Jason’s mother.
-Clark seems to have gotten over Alicia too quickly. The Chloe part of the last story gets more exploration but otherwise the previous episode might as well not have happened. Still, it's a great episode with a character growth moment for Clark. He gets the chance to see what using his powers frivolously would initiate which sets him once again on the path to becoming a superhero. It's a nice payoff to the whole football idea.
14) Krypto
Thieving super dogs, what’s next? Experimental animals are being used by criminals. A dog escapes and runs into Lois. He’s taken in by the Kents which, of course, draws Clark into the criminal plot.
-I can’t believe they actually worked in the super dog. As cheesy as it sounds, though, it’s a pretty good episode. Smallville-worthy explanations are given to everything.
15) Sacred
Upon his death Swann returns the key to Clark (how he got it in the first place was never explained). Jor El sends his son on a mission to find the remaining stones before any humans do. Using the excuse of protecting Lana he accompanies her to China as she chases Lex and Jason who have gone on their own stone hunt. China holds many surprises for them all.
-While exciting as far as action, this episode falls heavily into the weak stones/witches story-arcs. The whole idea of a stone hidden in a Chinese temple along with the clues that are left is far-fetched even for a show like Smallville.
16) Lucy
Lois’ little sister is coming for an impromptu visit. There is tension between the siblings, and soon Clark finds out the younger Lane is in deep trouble with some dangerous people.
-This has some good background about Lois' childhood and family life.
17) Onyx
A lab accident splits Lex into good and evil entities. With plenty of metaphor to go around evil Lex incarcerates the good one then sets out to wreck the lives of everyone they know.
-This is typical of Smallville's odd situations for its characters.
18) Spirit
Why is Chloe trying to ax Jonathan to death? Let’s go back a day and find out. Dawn is the pinnacle of popular dumb blond-icity, and she hates Chloe for running against her for prom queen. Wait, what? Chloe for prom queen? Dawn soon learns that she has an edge over her adversaries, and she will be queen no matter what.
-The band Lifehouse gets a little screen time.
19) Blank
A guy walks into the Talon, robs it, then blanks the minds of those that saw him. When Clark confronts the guy he blanks the fledgling hero’s mind. With the Kents out of town it’s up to Chloe to keep Clark out of trouble and bring him back up to speed figuratively and literally. They also want to unravel the mystery of the memory stealer.
-While it’s a bit of a cheat to do the amnesia thing again in the same season they at least don’t ignore the fact that it’s happened already.
20) Ageless
A girl gives birth to a nuclear explosion, kind of. Lana and Clark find themselves watching after a young boy who ages with bursts of energy. Soon he will release enough energy to kill all those around them unless Clark can find a way to stop it. Meanwhile, he learns a little of what it’s like to be a father.
-A little slow as far as action, but an emotion filled episode. It's loses some punch by being so similar to the Ryan stories, but it's still pretty good.
21) Forever
Chloe finds her school suddenly deserted. She’s trapped in an alternate reality of sorts where failure to comply with the rules results in horrible consequences.
-A weak episode with some inconsistencies (when Chloe comes out of her frozen state she can’t tell anything happened, but when Lana comes out of hers she gasps like she is out of breath).
22) Commencement
Everyone’s in a final race to get those stones. It’s down to the wire for Clark, but he’s already waited too long; his hesitance has set into motion a new meteor shower that will have far more dire consequences than anyone could realize.
-Despite my dislike of the stones story arc, the payoff here is pretty exciting.