B5 was perhaps the best written and underrated science fiction to be aired on television, light years ahead of its time (and with some debate perhaps it arrived ahead of its time). G'kar, the story arc for him from start to finish was amazing, the transition was perfect in my opinion. And getting even better the speeches they gave were the most memorable ones to date, like this for example. You had action sequences which had emotional weight, for example the episode severed dreams (i think it was that, when B5 leaves the earth alliance) you only met the guest characters for like 15 minutes yet I actually cared. SGU characters the fact that I'm wishing harm on them is an obvious sign.
Edit: The way how the alien races interacted with each other was also good, the culteral differences (like when lennier and vir moments were funny) Kosh, Vorlons perhaps the best enigmatic race and the shadow's the best villian both of which had methods of influence and the worst part of it all, neither side was right, each one you could agree with.
Also best speech ever!
http://www.youtube.com/watch?v=DPjmxIWLEaU
The acting is also superb, the look of regret on Londo and the broken but defiant G'kar, freaking awesome.
Now I'm depressed, clinging onto an empire that has long since fallen to the petty squablings of teenage romance and angst, next episode on SGU, genital warts.