N.B. this has been written at that point in time when all of
Season 3 has been aired and details of the first episode of Season 4
have been revealed. It is assumed that readers will have at least a
similar level of knowledge with regards to the series, those who haven't
seen these episodes (or at least haven't followed the spoiler pages) may
wish to avoid reading this in order to not become aware, or spoiled, of
certain 'future' events in the series they have yet to see.
"I see the First Ones, lately, much more clearly,
Spilling blood along the turning ground..." - Caroline Lavelle, 'Turning Ground'.
After three years of Babylon 5 running it is perhaps now a good time to step back and look at the trends emerging from the series. One of the wonderful attractions of the series for me is knowing that the creator has a story all planned out and is dropping hints as to the overall story as we go along. I just love this kind of puzzle.
It is now that I think I am begining to see JMS tipping his hand on where the show is going. He has a nasty habit of having what are not so wonderful foreground stories in an episode with some fairly important stuff hidden away. 'Grey 17 is missing' is one of them and I would rate 'Passing through Gethsemne' as one as well. I expect 'A Late Delivery from Avalon' will be likewise, once I get a chance to see it.
In 'Passing through Gethsemne' he introduces the Minbari concept of the universe being aware and trying to understand itself. 'Grey 17 is missing' expands on that idea bringing in the idea of perfection, that once the universe does understand itself it will begin anew with a more complicated and glorious puzzle to solve. You also have the pointers to the humans being special because they seem to be the middle ground between the Vorlon and Shadow view.
(This might explain why Sheridan is the first entity to get so far and so close in reaching Lorien, although desperation and the suicidal nature of his act might factor in here as well.)
Essentially the Vorlons beleive in order, co-operation and structured progress, without realising the stagnating effect that has. The Minbari, the most strongly influenced by the Vorlons, show every sign of having a stagnating culture. Their technology and methods have not improved markedly from a thousand years ago , rather than revolutionary change they have had gradual change and advancement in skill and technology while their society begins to unravel more and more.
However with the Shadows their method is competition , harsh and fierce but fast at producing rapid advancement as each side desperately tries to advance enough to gain the upper hand. Ultimately their method suffers in that it is wholy destructive and once there is only one surviving race then they get into the problem that that race is too dominant and without a reason for further development, again stagnation results. We see this with their chosen first ally, the Centauri.
In the history JMS has given us the Centauri quickly rose to power and dominated the galaxy for a time, only the more advanced Minbari and Vorlons with their seemingly isolationist policies escaped the net the Centauri cast. And yet what did they do with their spoils once they had them? Their empire declined and all that they accomplished they lost as their lives became comfortable and the urge to fight was forgotten. Stagnation, worse than that - decline - resulted.
I conclude that only one approach will succeed, that of the inbetween road. The race that would go further than either the Minbari or the Centauri, perhaps even further than either the Vorlons or Shadows, has to be one that is capable of ordered progress when the circumstances demand it but also has to be capable of revolutionary change from within - of internal conflict. Of all the races depicted on B5 only one shows this ability and only one has been described by the other aliens as being so confusing for it.
Londo has frequently described how often the humans are fighting amongst themselves and that it is a wonder they get anything done. Delenn has talked of the wonder and amazement of the humans ability to make cohesive communities out of disperate populations and reach towards a single goal while at the same time not loosing their individuality. G'kar has realised that the humans are the key to the war and on both sides we see that the respective elder races have chosen humans as their tacticians and planners.
Exactly what is going on and as to why the Vorlons and Shadows seem
to be fighting this interminable war between their two viewpoints is
not something we have enough clues to understand yet. JMS is still
hiding some cards. That both of their approaches have failings has been
in evidence for sometime now. The Shadows with their hit and run
attacks and overly uncaring attitude to life clearly have problems. That
the Vorlon's way has problems has been given to us by a small clue
dropped since Season 2, the Minbari Grey Council's mantra.
Namely :- 'We are the Grey, we stand between the star and the candle.'
Given the Minbari's crucial role in the previous Shadow war the star and the candle now seem likely to mean the Vorlons and the Shadows respectively. It is interesting to note that it was a human, Sinclair, who formed the Grey Council and handed it it's mantra - once again a human is taking a crucial role in organising and planning. 
At any-rate, even though it hasn't been fully revealed, both the Vorlons and the Shadows have come short in some way, against some measuring scale. If we entertain the thought for the moment that the Vorlons were lying to us when they described the Shadows as the most ancient of enemies that the First Ones fought, then an interesting possibility opens up. Consider the Vorlon and Shadow technology for a moment, both races use organic technology and in the one engagment we have seen the two seemed fairly evenly matched in abilities when it comes to fighting.
I contend that the two races are of similar age, and similar advancement. That the Vorlons are not so much the last of the First Ones as they claim, but rather one of the last remaining along with the Shadows. We know that the First Ones have largely moved on to contemplate realms and topics of a more abstruse nature than the mere galaxy can provide information on. Consequently what if the two races have been deliberately locked into the Galaxy by the First Ones and instructed that the conditions of their release is to advance the younger races to a certain level.
This would explain why the First Ones still pop in to the Galaxy occasionally, to check in on how the two are behaving. It would also explain why there is, seemingly, a First One living deep inside Z'ha'dum who claims that the Shadows, and the Vorlons, come there because of him in some fashion. 
Perhaps even more wild is the idea that the First Ones, all of them, are limited in some way from achieving the next stage due to their inability to act together without sacrificing their individuality. A trick that seemingly only humans have developed. Certainly the bona fide First Ones that we have seen have not shown any emotional maturity commensurate with their level of technical advancment.  Perhaps the humans are not so much the key to Vorlon and Shadow release from the Galaxy but more the key to the final self understanding of the universe and it's preperation for the next stage. Could that be what 'Sleeping in the Light', one of two possible titles of the very last episode of season 5, refers to?
Still, these are my thoughts for the moment. Hopefully JMS has outwitted me and is giving me mis-leading, but consistant, clues...
 Taken from 'War Without End' where we are given glimpses of the Minbari ships and people of a thousand years ago. Their ships were instantly familiar seemingly longer and more elongated versions of what they use now.
 This is referenced from 'Z'ha'dum' where Sheridan meets with his counter part working for the Shadows.
 Also referenced from 'War Without End' where, in the closing scenes, it is revealed that Valen, the Minbari not born of Minbari, is indeed Sinclair transformed by a chrysalis device similar to what Delenn used at the end of Season 1.
 Taken from 'Hour of the Wolf' the first epsiode of Season 4.
 As seen in 'Voices of Authority' where an elder race is emotionally duped into helping in the fight by tactics and words last seen on a kindergarden playground. Even the original Kosh's behavior in 'Interludes and Examinations' is more akin to that of an unruly teenager than a member of an elder race of great maturity.
Perhaps we simply have caught these individuals on a bad tentacle day or something...