First let me state what I do not love:
1. The sets. They are cheap and unimaginative. However, they blew most of their budget on costumes and effects, and cheesy sets are a staple of sci-fi, so....
2. The effects. The special effects are TERRIBLE. Seriously. But they were one of the first tv shows to use massive cgi every week, so maybe it's excusable. *thinks* No, no, not entirely. It's just bad.
What I LOVE:
1. The storyarc. 5 seasons of one continuous storyline. Ok, granted, season 5 is a little out of sync, because they didn't know they were going to get that one. I think it still works well, however. This storyline does not make for good episodic viewing--if you miss 1 episode, you miss crucial information; but this makes for superb DVD viewing. It's more like a miniseries than a tv show.
2. The characters. The characters move through very believable arcs, and not every good guy ends up happy oy dead (the two usual options). Some end up broken, some end up isolated. Many of them do survive to lead happy lives, but not always the ones you'd expect. Some characters that began as loveable rogues become despicable power-grubbers and then degenerate into pitiable men who cannot tell right from wrong even when they want to. Some begin as violent rebels, and become wise, strong, leaders. And then you have Mr. Morden, a man so evil that his smile can send you running for cover (I am not exaggerating, his smile is incredibly creepy).
3. The costumes. They are lovely, imaginative, and very distinct between the 10 major people groups of the B5 universe.
Incidentally, I still don't own seasons 1 and 5, and my birthday is on Monday...not to hint, or anything... :)