I am not a Northwest Airlines fan. I think the product in both the premium and economy cabins is inferior, planes generally older, although NW does have a substantial fleet of 757's and A320/A319's, and some of the 744's are newer, but agree that by and large, the cabin crew are friendly and helpful.
Northwest has opted not to acquire vast numbers of new planes to keep its balance sheet in check. However, overall, Northwest offers a basic product and is outdone by virtually all other US airlines flying to Europe in on-board amenities, comfort, and breadth of services.
For $240 R/T, I'd probably fly NW too, but spend the entire journey wishing I was on US, CO, DL, BA, AF, or some other airline.