I'm already 2/3 of the way through Season 4. It's gotten to the point that I'm limiting myself to one episode every other day. If I don't I'll be jonesing WAY to soon.
Quality-wise it's an exceptional set that's on par with the other three season releases, sharing the same strengths and weaknesses. Strengths: Video, audio, commentary. Weaknesses: Digital effects shots still look crappy, and there are a LOT of them in Season 4. But, if you're a B5 fan you know you're gonna buy it anyway.
My discs were all sound and happy on their hubs, I'm pleased to report. Man this has some great bass....when the Island is blown up about ep. 6, it's really devastatingly loud and low.