I don't know about Northwest flight crews on international routes, but I have flown all kinds of domestic routes on Northwest as I live near Detroit, soch as DTW-FLL, DTW-SFO, DTW-MCO, DTW-PBI, DTW-DCA, and MSP-DTW on 727s, 757s, DC10s, 320s, DC9s, and 319s. Honestly, I will give you the 411 on Northwest. The food service is mediocre but steadily improving. In-flight entertainment sucks big time...one movie internationally and re-runs of "Dharma&Greg" and the like on domestic 757 flights (like DTW-DEN is usually a 757) Detroit's airport is miserable no matter if you live here or connect here. You might get your days exercise going from one gate to another. The planes are old, but lots of them have newer interiors (especially the DC9s, DC10s, and some 757s) but the 727s are dingy. The 319s are brand new and the A320s are recent if not brand new. Northwest has gone a decade since their last serious accident (pilot error) and the plane type involved (the MD-80) no longer is used at NW. I believe their maintenance is first-rate, and the planes are old because they couldn't order new ones while they were in Chapter 11 for much of the first third of the nineties ('90-'94)
As for the flight attendants, I have encountered no flight attendant that has been rude to me. My negative experiences with Northwest have ALL been with the ground crew in Detroit (gate agents, CSRs, etc...) Almost every flight I am on there is one very attractive flight attendant, and yes, almost invariably one older flight attendant. There also seems to be a great amount of diversity amongst FAs (I respect that)...lots of male FAs also (different from other airlines)...
Northwest and Continental is all I will fly because A) I live in Southeastern Michigan and B) they are a known-quantity; I haven't flown with anyone else since 1997 (with Continental). Give them a shot if the airfare is right.