I really liked B5 when it originally aired. It has some great characterization and subplots, though IMO the series was quite uneven. I think they could have done it in four seasons or less and it would have been much better.
Supposedly the entire story was planned start to finish in advance, but I stopped believing that after season 3. I think there may have been *a* story which was written start to finish, but I can't shake the feeling that at some point about halfway through the airing that the story was reworked in order to spread it out over another couple of seasons.
But if you're a sci-fi fan, then you should definitely watch B5. It would be great if there was a guide somewhere on the net that would list the "core" episodes that you could watch to get the main story, without all the chaff.