Part of the reason it is so action packed was because there was no guarantee that the show was going to get its fifth season, so stories were 'accelerated' to make sure the story JMS wanted was told.
Picking up from the season three (and my all time favourite) cliffhanger, Z'ha'dum we soon find out what became of Sheridan and Garibaldi, and we finally get to meet Emperor Cartagia on Centauri Prime.
The Shadow War changes pace with the Vorlons taking out Shadow influenced worlds and the Shadows returning form. Sheridan forces a showdown between the two powers which brings the conflict to an end as they step aside.
In the 'quiet' time mid-season, we are reminded of the problems on Earth with the arrival of an ISN news crew, the embargo placed on Babylon 5 becoming ever tighter, Marcus and Franklin head to Mars to make contact with the Resistance.
Conflict comes to Minbar and sees Delenn involved in what's going on there as a result of breaking the Grey Council a year prior. We meet the Drakh, who we learn were servants of huge Shadows before they left. Delenn and Neroon resolve their differences to reunite Minbar.
Finally, a news report documenting atrocities by Earthforce personnel on civilian targets prompts Sheridan to take action and liberate Earth and her colonies from President Clark.
Our characters go through some major changes. G'Kar risks his sanctuary in search of Garibaldi and ends up captured and brought to Centauri Prime. Only then is he able to forge a deal with Londo - both who want to save their worlds.
Sheridan returns from the dead and Z'ha'dum with Lorien, proposes to Delenn, confronts the Vorlons and the Shadows and leads the liberation of Earth. Garibaldi returns and things seemed normal at first until the Shadow War ended and he resigned as Head of Security. He and Sheridan soon butt heads often, driving a wedge through their relationship. It's not until the end of the season we realise what has happened to Michael.
Marcus and Franklin head to Mars to contact the Resistance there in preparation for the retaking of Earth and Ivanova becomes the face of the Voice of the Resistance, then taking over command of the liberation fleet from Sheridan when he's captured. Ultimately, Marcus gets to show his love for Ivanova.
There are so many action packed episodes in this season including most of the episodes at the beginning and end. The Summoning is always a standout for me as it introduces the Vorlon Planet Killer, Falling Toward Apotheosis confronts the Vorlon Ambassador and The Long Night and Into the Fire finish up the conflict. Lines of Communication introduces a new race to watch out for in the Drakh and Moments of Transition finalises the Minbari conflict while being the prelude to the Liberation of Earth through No Surrender, No Retreat to Endgame.
While there are many high scoring episodes in this season, there's also The Illusionof Truth which for me, is probably my least favourite episode of the series and there are some more 'experimental' episodes such as Intersections in Real Time and The Deconstruction of Falling Stars.
In the middle of the season, the second movie Thirdspace takes place. Thirdspace is a standalone event but features some decent back story to the Vorlons and their discovery of another realm ruled by a dangerous race hellbent on destroying everything.
Overall, season four rates fairly well with an average score of 7/10 per episode. Including the lowest score awarded to a Babylon 5 episode so far, a 5/10 for The Illusion of Truth, season four gains from Into the Fire, Moments of Transition, The Face of the Enemy, Between the Darkness and the Light and Endgame all scoring 8's.
With the wars and conflict over, it's hard to think what Season Five can offer but some of this was previewed in the season four finale The Deconstruction of Falling Stars.
The Wheel of Fire awaits...