For any true Babylon 5 fan, The Gathering is indispensable. With such a long and detailed story arc ahead, it would be a mistake to miss this, or the majority of the episodes of the first season. Unfortunately, both suffer from mediocre acting and so-so special effects (by today's standards).
By the end of season 1, Michael O'Hare does grow on you, even with his hammy acting (he is a stage actor which didn't translate so well to TV). He's not bad, but Bruce Boxleitner ultimately does a much better job. Claudia Christian also gets better over time, and is light years ahead of Tamlyn Tomita, who did an awful job in the pilot.
That said, I am on my second viewing of B5, and although the pilot and first season are cringe-worthy at times, they are both worth seeing, culminating in an incredible payoff with seasons 2,3 and 4. Watch this and then watch the whole series. You won't be disappointed.