Murphy benefitted from an unusual cross-party endorsement from Republican ex-Rep. Mike Fasano, whose appointment to a county-wide post prompted this special election in the first place, and who was furious at a misleading attempt by Gunter allies to make it seem as though he'd endorsed him. This was also the first partisan election in the country following the federal government shutdown; while it's not certain whether that played a role, it couldn't have helped Republicans.
Democrats are now up to 45 seats in the House, though they remain in a big hole, with the GOP still controlling 75. But another positive sign for Democrats is that Barack Obama carried this seat 52-47 last year, so despite running in an October special in an odd-numbered year, Murphy was barely off the president's pace. It'll be a long slog back to the majority, but Murphy gives her party a good place to start.