I worked for a big ecommerce company in Luxembourg for about two years and I had a great time there. That said, obviously it depends on what you expect or with which city you compare Luxembourg. It's a small town by the standards of many of the other cities in this app.
But there is a high diversity of expats. Nearly 40% of the population is foreign born and many of them love Luxembourg for it's "quality of life". Much of this has to do with the country’s wealth. I think it has the highest GDP per head in the world. Do you enjoy a life with family and friends and the outdoors, Luxembourg might be great. You are looking for an urban environment with night life, vibrant culture and art scenes, then you might say it's dull.