While the episodes are pretty self contained, and can be watched individually BGC does have an overall story arc, it just takes a break from it in episodes 4, 7, and 8.
The AD Police manga, and BGC episodes 1, 2, 3, 5, and 6 are all part of a larger storyline arc that was supposed to be resolved in the last five episodes, involving the relationship between Sylia and Mason/Largo.
I've heard that BGCrash was a heavily edited/condensed version of the original last five episodes, but to be honest I watch BGCrash episode 1 once and never had the stomach to finish the series.