I was actually a passenger onboard NW99/25SEP MSP-HNL which had to air return back to MSP due center gear door failed to retract after take-off. Attempts by crew to correct this item after consulting with NW maintenance via radio failed...thus precluding flight from continuing onto HNL. Aircraft was too heavy for landing...therefore we "dumped" fuel for about 15 minutes or so...while doing circles around 7000 feet. Although Captain said our return was not considered an "emergency", it was standard airport operating procedure to have airport crash fire rescue present for any aircraft returning to field. Therefore, upon landing, airport crash fire rescue vehicles were present but quickly went back to base once our landing was "routine". Pulled back into MSP gate F-10 about an hour after we originally departed. The "fix" was quite fast...some kind of indicator light was the reason given. One pilot was borderline with his crew duty time...so a replacement pilot was called in. Aircraft was re-fueled...then we waited until this replacement pilot arrived. Once he arrived, those passengers who elected to deplane were reboarded...and we pushed back again around 240pm (3hrs late)...and was airborne again shortly before 3pm local time. Due favorable winds (scheduled flight time 7hr39min), we made up some time enroute and arrived in HNL around 525pm (just over 2 hours late). DC-10 on today's flight was N234NW. Despite delay, IMO NW handled this delay well and provided timely updates.