The Gathering (1993)
Dir. Richard Compton
A feature–length pilot that's notable mostly for setting up large chunks of the story arc that would help make Babylon 5 one of TV's best ever sci-fi series in subsequent years, although no one but series creator J. Michael Straczynski and the producers really knew back then because such long-running continuity wasn't the norm at the time.
Some of the acting is weak, but a few of the cast were replaced when the series went into production.
If you know B5 already, then The Gathering is worth hunting down, despite its flaws.
If you're new to the station, however, or not sure if a plot-heavy sci-fi show is really for you, it might be better to start with Season 1 of the TV series instead, even though it means missing out on some crucial back-story for certain characters. You can fill in the gaps later, but be aware that there are a number of notable differences between what was planned and what eventually came to pass.