The first season was a mixture of hits and misses. The tone WAS different to TNG, which pleased some but not others.
The series is now entering its 7th and final year. There have been many changes over that time, but first, an episode list.
In my opinion, the switch to the Dominion war in the latter half of series 5 and series 6 was an error. Responding to the success of Babylon 5- particularly the critical success, DS9 was given an "arc". Now Sisko and co were fighting a war- cue all those tired old war cliches and cheap emotions. Trek has always had the failing of being a touch preachy, but I found the switch in emphasis to plot rather than character a turn off. Nana Visitor's real life pregnancy affected series 5, she and fellow DS9 actor Alexander Siddig had a son together. But this lead to a plot device involving Kira carrying the O'Brien's child- unlikely and restrictive for this most lively character.
In terms of character, the biggest change was the addition of TNGs Worf, at the beginning of series four. A shot in the arm was needed, but I never was comfortable with him on DS9- he was a TNG character, and the romance between him and Dax was completely unbelievable to me. Avery Brooks continued to impersonate a piece of wood, despite a new haircut, and was at his best as a director- "Rejoined" being one of the best episodes, and one that tackled and interesting issue.
Series One
Series Two
Series Three
Series Four
Past Prologue
A Man Alone
Babel
Captive Pursuit
Q Less
Dax
The Passenger
Move Along Home
The Nagus
Vortex
Battle Lines
The Storyteller
Progress
If Wishes Were Horses
The Forsaken
Dramatis Personae
Duet
In the Hands of the ProphetsThe Homecoming
The Circle
The Siege
Invasive Procedures
Cardassians
Melora
Rules of Aquisition
Necessary Evil
Second Sight
Sanctuary
Rivals
The Alternate
Armageddon Game
Whispers
Paradise
Shadowplay
Playing God
Profit and Loss
Blood Oath
The Maquis (I)
The Maquis (II)
The Wire
Crossover
The Collaborator
Tribunal
The Jem'HadarThe Search (I)
The Search (II)
The House of Quark
Equilibrium
Second Skin
The Abandoned
Civil Defense
Meridian
Defiant
Fascination
Past Tense (I)
Past Tense (II)
Life Support
Heart of Stone
Destiny
Prophet Motive
Visionary
Distant Voices
Through The Looking Glass
Improbable Cause
The Die Is Cast
Explorers
Family Business
Shakaar
Facets
The AdversaryThe Way of the Warrior
The Visitor
Hippocratic Oath
Indiscretion
Rejoined
Little Green Men
Starship Down
The Sword of Kahless
Our Man Bashir
Homefront
Paradise Lost
Crossfire
Return to Grace
The Sons of Mogh
The Bar Association
Accession
Rules of Engagement
Hard Time
Shattered Mirror
The Muse
For the Cause
To The Death
The Quickening
Body Parts
Broken LinkSeries Five
Series Six
Series Seven
Apocalypse Rising
The Ship
Looking For Par'Mach In Al...
..Nor The Battle To The Strong
The Assignment
Trials and Tribble-ations
Let He Who Is Without Sin....
Things Past
The Ascent
Rapture
The Darkness and the Light
The Begotten
For the Uniform
In Purgatory's Shadow
By Inferno's Light
Doctor Bashir, I Presume?
A Simple Investigation
Business As Usual
Ties of Blood and Water
Ferengi Love Songs
Soldiers of the Empire
Children of Time
Blaze of Glory
Empok Nor
In the Cards
A Call to Arms
A Time to Stand
Rocks and Shoals
Sons and Daughters
Behind the Lines
Favor the Bold
The Sacrifice of Angels
You Are Cordially Invited...
Resurrection
Statistical Probabilities
The Magnificent Ferengi
Waltz
Who Mourns for Morn
Far Beyond the Stars
One Little Ship
Honor Among Thieves
Change of Heart
Wrongs Darker Than Death
Inquisition
In the Pale Moonlight
His Way
The Reckoning
Valiant
Profit and Lace
Time's Orphan
The Sound of Her Voice
Tears of the Prophets
Shadows and Symbols
Afterimage
Take Me Out to the Holosuite
Chrysalis
Generally, DS9 hit its peak in the middle series, numbers, 2 to 5.
Probably the best episode of the entire series was "Trials and Tribble-ations", a simply brilliant homage to the original Trek series, that features perfect blending of film so that O'Brien, Dax, Sisko and Bashir look as if they are right there with Kirk and co. Dax looked FAB in the Trek minidress, and even Sisko suited the old gold jumper. A lovely mix of humour and plot that sadly the the series achieved all too infrequently. Other hits, for me anyway, were those with Kira and the Bajorans. Like the Klingon stories in TNG, these were a matter of taste, and the Bajoran stories were a fairly obvious metaphor for the Jewish people. However, I liked the politics, and the wonderful Louise Fletcher made a brilliantly creepy baddie, Kai Wynn. Less successful were the endless allusions to baseball and Sisko's love life (YAWN). Also, the Ferengi episodes were a but dull, as was Odo's quest for his people. Dax was all to frequently under used, as was the excellent Colm Meany as O'Brien. Bashir stayed as irritating as ever, although a rather amusing James Bond style story "Our Man Bashir" was much more fun.
DS9 limps towards its finale having lost a major character- Terry Farrell has had enough and Jadzia leaves dramaticaaly at the end of series six. In my view, this incarnation of Star Trek will be one remembered for a few high points, but generally as a disappointment.