I nominate Firefly. Fantastic, swashbuckling neo-western-space-opera incredibilicity: nearly ruined by some warbling, drawling schmuck who writes far better dialogue than lyrics.
Second nomination: Blake’s 7. Interminable introduction in the first place, but if you watch the later seasons, you get to watch two introductions! Not only are they both stupor-inducingly long, but they’re nearly identical! Argh!