Parliament of Dreams: is a shining, shining example of what's best about B5 this early on. It introduces two more regulars - Lennier and Na'Toth, starts their relationships with their respective ambassadors, showcases one of JMS' strengths - giving different aliens their own cultural backgrounds and religions, and using humanity's own, and managing to avoid to present any of them as superior to the other -; but most of all, this is the episode which starts to flesh G'Kar out as a character.
Until then, we did get some background information on G'Kar that made his motivations understandable - i.e. the century of Centauri occupation on Narn - but we only ever saw him from other characters' povs, and his function in the narrative seemed to be a sometimes funny villain. Parliament of Dreams brings us in G'Kar's pov and without suddenly making him a saint shows us there is much more going on with him. There is also some neat foreshadowing, whether or not that was intentional at this early point.
G'Kar refusing to scream for the assassin is an obvious parallel to G'Kar refusing to scream for Emperor Cartagia in s4. It's all the more effective because the episode showed earlier that G'Kar has a healthy sense of self-preservation and is indeed afraid for his life. His bravery, endurance and stubbornness isn't because of a complete lack of fear, it's despite the fact he wants to live as much as anyone. The episode also showcases G'Kar's joie de vivre (when not being threatened); him singing to his food was a brilliant stroke (and as I seem to recall an addition by Andreas Katsulas?). It's picked up much later in s3 in a far more twisted context, when he's locked in a turbo lift with Londo.
Parliament of Dreams is the episode that gives us more about the Narn than just the fact they're the current rising power and former victims of Centauri occupation. They seem to have gender quality (Na'Toth, like Ko'Dath before her, wears the same type of body armour G'Kar does and is certainly talking to Tu'Pari as an equa), a ruling council instead of a sole head of state, and, interestingly, an assassin's guild with strict rules. (This is interesting because given that the Centauri have something very simular - they seem to have guilds for everything, including torturers, who as Cartagia complaints insist on the new name pain technicians - I rather suspect the Narn adopted this from them during that century of occupation.)
As far as the attachés are concerned: it was a stroke of luck the actress for Ko'Dath didn't cope with the Narn make-up, because Julie Caitlin Brown is brilliant as Na'Toth, giving her a sardonic sense of humour and exuding intelligence; her toughness comes across as impressive, not as a caricature as with the earlier attaché. And it's my ongoing regret she didn't stay; Mary Kay Adams simply wasn't as good as Na'Toth, and so it's not surprising JMS eventually wrote her out. I'm still torn as to whether or not this benefited or lessened the overall story - on the one hand, Na'Toth returning to Narn heightens G'Kar's isolation, and makes his breakdown-plus-epiphany-plus-path-to-wisdom in season 3 all the more effective. And of course finding her a Centauri prisoner in s5 was an effective way of demonstrating that just because he found wisdom, he doesn't feel less fiercely about this type of outrage. On the other hand, if Na'Toth had remained on the station, the relationship between her and G'Kar might have become the equivalent of the one between Londo and Vir in terms of emotional importance, and it would have provided us with an alternate Narn pov on events, and more background information on the Narn.